diff --git a/beta/src/content/apis/react/Children.md b/beta/src/content/apis/react/Children.md
index ce3019d65..06cef1ae7 100644
--- a/beta/src/content/apis/react/Children.md
+++ b/beta/src/content/apis/react/Children.md
@@ -1,20 +1,939 @@
---
-title: React.Children
+title: Children
---
-
+
-This section is incomplete, please see the old docs for [React.Children.](https://reactjs.org/docs/react-api.html#reactchildren)
-
-
+Using `Children` is uncommon and can lead to fragile code. [See common alternatives.](#alternatives)
+
-`React.Children` provides utilities for dealing with the this.props.children opaque data structure.
+`Children` lets you manipulate and transform the JSX you received as the [`children` prop.](/learn/passing-props-to-a-component#passing-jsx-as-children)
-See the [React.Children](https://reactjs.org/docs/react-api.html#reactchildren) docs for more info.
+```js
+const mappedChildren = Children.map(children, child =>
+
+ {child}
+
+);
+
+```
+
+---
+
+## Usage {/*usage*/}
+
+### Transforming children {/*transforming-children*/}
+
+To transform the children JSX that your component [receives as the `children` prop,](/learn/passing-props-to-a-component#passing-jsx-as-children) call `Children.map`:
+
+```js {6,10}
+import { Children } from 'react';
+
+function RowList({ children }) {
+ return (
+
+ {Children.map(children, child =>
+
+ {child}
+
+ )}
+
+ );
+}
+```
+
+In the example above, the `RowList` wraps every child it receives into a `
+
+
This is the first item.
+
+
+
This is the second item.
+
+
+
This is the third item.
+
+
+```
+
+`Children.map` is similar to [to transforming arrays with `map()`.](/learn/rendering-lists) The difference is that the `children` data structure is considered *opaque.* This means that even if it's sometimes an array, you should not assume it's an array or any other particular data type. This is why you should use `Children.map` if you need to transform it.
+
+
+
+```js
+import RowList from './RowList.js';
+
+export default function App() {
+ return (
+
+
This is the first item.
+
This is the second item.
+
This is the third item.
+
+ );
+}
+```
+
+```js RowList.js active
+import { Children } from 'react';
+
+export default function RowList({ children }) {
+ return (
+
+ {Children.map(children, child =>
+
+ {child}
+
+ )}
+
+ );
+}
+```
+
+```css
+.RowList {
+ display: flex;
+ flex-direction: column;
+ border: 2px solid grey;
+ padding: 5px;
+}
+
+.Row {
+ border: 2px dashed black;
+ padding: 5px;
+ margin: 5px;
+}
+```
+
+
+
+
+
+In React, the `children` prop is considered an *opaque* data structure. This means that you shouldn't rely on how it is structured. To transform, filter, or count children, you should use the `Children` methods.
+
+In practice, the `children` data structure is often represented as an array internally. However, if there is only a single child, then React won't create an extra array since this would lead to unnecessary memory overhead. As long as you use the `Children` methods instead of directly introspecting the `children` prop, your code will not break even if React changes how the data structure is actually implemented.
+
+Even when `children` is an array, `Children.map` has useful special behavior. For example, `Children.map` combines the [keys](/learn/rendering-lists#keeping-list-items-in-order-with-key) on the returned elements with the keys on the `children` you've passed to it. This ensures the original JSX children don't "lose" keys even if they get wrapped like in the example above.
+
+
+
+
+
+The `children` data structure **does not include rendered output** of the components you pass as JSX. In the example below, the `children` received by the `RowList` only contains two items rather than three:
+
+1. `
This is the first item.
`
+2. ``
+
+This is why only two row wrappers are generated in this example:
+
+
+
+```js
+import RowList from './RowList.js';
+
+export default function App() {
+ return (
+
+
+
+ );
+}
+```
+
+```js RowList.js
+import { Children } from 'react';
+
+export default function RowList({ children }) {
+ return (
+
+ {Children.map(children, child =>
+
+ {child}
+
+ )}
+
+ );
+}
+```
+
+```css
+.RowList {
+ display: flex;
+ flex-direction: column;
+ border: 2px solid grey;
+ padding: 5px;
+}
+
+.Row {
+ border: 2px dashed black;
+ padding: 5px;
+ margin: 5px;
+}
+```
+
+
+
+**There is no way to get the rendered output of an inner component** like `` when manipulating `children`. This is why [it's usually better to use one of the alternative solutions.](#alternatives)
+
+
+
+---
+
+### Running some code for each child {/*running-some-code-for-each-child*/}
+
+Call `Children.forEach` to iterate over each child in the `children` data structure. It does not return any value and is similar to the [array `forEach` method.](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/forEach) You can use it to run custom logic like constructing your own array.
+
+
+
+```js
+import SeparatorList from './SeparatorList.js';
+
+export default function App() {
+ return (
+
+
This is the first item.
+
This is the second item.
+
This is the third item.
+
+ );
+}
+```
+
+```js SeparatorList.js active
+import { Children } from 'react';
+
+export default function SeparatorList({ children }) {
+ const result = [];
+ Children.forEach(children, (child, index) => {
+ result.push(child);
+ result.push();
+ });
+ result.pop(); // Remove the last separator
+ return result;
+}
+```
+
+
+
+
+
+As mentioned earlier, there is no way to get the rendered output of an inner component when manipulating `children`. This is why [it's usually better to use one of the alternative solutions.](#alternatives)
+
+
+
+---
+
+### Counting children {/*counting-children*/}
+
+Call `Children.count(children)` to calculate the number of children.
+
+
+
+```js
+import RowList from './RowList.js';
+
+export default function App() {
+ return (
+
+
This is the first item.
+
This is the second item.
+
This is the third item.
+
+ );
+}
+```
+
+```js RowList.js active
+import { Children } from 'react';
+
+export default function RowList({ children }) {
+ return (
+
+
+ Total rows: {Children.count(children)}
+
+ {Children.map(children, child =>
+
+ {child}
+
+ )}
+
+ );
+}
+```
+
+```css
+.RowList {
+ display: flex;
+ flex-direction: column;
+ border: 2px solid grey;
+ padding: 5px;
+}
+
+.RowListHeader {
+ padding-top: 5px;
+ font-size: 25px;
+ font-weight: bold;
+ text-align: center;
+}
+
+.Row {
+ border: 2px dashed black;
+ padding: 5px;
+ margin: 5px;
+}
+```
+
+
+
+
+
+As mentioned earlier, there is no way to get the rendered output of an inner component when manipulating `children`. This is why [it's usually better to use one of the alternative solutions.](#alternatives)
+
+
+
+---
+
+### Converting children to an array {/*converting-children-to-an-array*/}
+
+Call `Children.toArray(children)` to turn the `children` data structure into a regular JavaScript array. This lets you manipulate the array with built-in array methods like [`filter`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/filter), [`sort`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/sort), or [`reverse`.](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/reverse)
+
+
+
+```js
+import ReversedList from './ReversedList.js';
+
+export default function App() {
+ return (
+
+
This is the first item.
+
This is the second item.
+
This is the third item.
+
+ );
+}
+```
+
+```js ReversedList.js active
+import { Children } from 'react';
+
+export default function ReversedList({ children }) {
+ const result = Children.toArray(children);
+ result.reverse();
+ return result;
+}
+```
+
+
+
+
+
+As mentioned earlier, there is no way to get the rendered output of an inner component when manipulating `children`. This is why [it's usually better to use one of the alternative solutions.](#alternatives)
+
+
+
+---
+
+## Alternatives {/*alternatives*/}
+
+### Exposing multiple components {/*exposing-multiple-components*/}
+
+Manipulating children with the `Children` methods often leads to fragile code. When you pass children to a component in JSX, you don't usually expect the component to manipulate or transform the individual children.
+
+When you can, try to avoid using the `Children` methods. For example, if you want every child of `RowList` to be wrapped in `
`, export a `Row` component, and manually wrap every row into it like this:
+
+
+
+```js
+import { RowList, Row } from './RowList.js';
+
+export default function App() {
+ return (
+
+
+
This is the first item.
+
+
+
This is the second item.
+
+
+
This is the third item.
+
+
+ );
+}
+```
+
+```js RowList.js
+import { Children } from 'react';
+
+export function RowList({ children }) {
+ return (
+
+ {children}
+
+ );
+}
+
+export function Row({ children }) {
+ return (
+
+ {children}
+
+ );
+}
+```
+
+```css
+.RowList {
+ display: flex;
+ flex-direction: column;
+ border: 2px solid grey;
+ padding: 5px;
+}
+
+.Row {
+ border: 2px dashed black;
+ padding: 5px;
+ margin: 5px;
+}
+```
+
+
+
+Unlike using `Children.map`, this approach does not wrap every child automatically. **However, this approach has a significant benefit compared to the [earlier example with `Children.map`](#transforming-children) because it works even if you keep extracting more components.** For example, it still works if you extract your own `MoreRows` component:
+
+
+
+```js
+import { RowList, Row } from './RowList.js';
+
+export default function App() {
+ return (
+
+
+
+
+
+ );
+}
+```
+
+```js RowList.js
+import { Children } from 'react';
+
+export function RowList({ children }) {
+ return (
+
+ {children}
+
+ );
+}
+
+export function Row({ children }) {
+ return (
+
+ {children}
+
+ );
+}
+```
+
+```css
+.RowList {
+ display: flex;
+ flex-direction: column;
+ border: 2px solid grey;
+ padding: 5px;
+}
+
+.Row {
+ border: 2px dashed black;
+ padding: 5px;
+ margin: 5px;
+}
+```
+
+
+
+This wouldn't work with `Children.map` because it would "see" `` as a single child (and a single row).
+
+---
+
+### Accepting an array of objects as a prop {/*accepting-an-array-of-objects-as-a-prop*/}
+
+You can also explicitly pass an array as a prop. For example, this `RowList` accepts a `rows` array as a prop:
+
+
+
+```js
+import { RowList, Row } from './RowList.js';
+
+export default function App() {
+ return (
+ This is the first item. },
+ { id: 'second', content:
+ );
+}
+```
+
+```css
+.RowList {
+ display: flex;
+ flex-direction: column;
+ border: 2px solid grey;
+ padding: 5px;
+}
+
+.Row {
+ border: 2px dashed black;
+ padding: 5px;
+ margin: 5px;
+}
+```
+
+
+
+Since `rows` is a regular JavaScript array, the `RowList` component can use built-in array methods like [`map`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/map) on it.
+
+This pattern is especially useful when you want to be able to pass more information as structured data together with children. In the below example, the `TabSwitcher` component receives an array of objects as the `tabs` prop:
+
+
+
+```js
+import TabSwitcher from './TabSwitcher.js';
+
+export default function App() {
+ return (
+ This is the first item.
+ },
+ {
+ id: 'second',
+ header: 'Second',
+ content:
+
+ );
+}
+```
+
+
+
+Unlike passing the children as JSX, this approach lets you associate some extra data like `header` with each item. Because you are working with the `tabs` directly, and it is an array, you do not need the `Children` methods.
+
+---
+
+### Calling a render prop to customize rendering {/*calling-a-render-prop-to-customize-rendering*/}
+
+Instead of producing JSX for every single item, you can also pass a function that returns JSX, and call that function when necessary. In this example, the `App` component passes a `renderContent` function to the `TabSwitcher` component. The `TabSwitcher` component calls `renderContent` only for the selected tab:
+
+
+
+```js
+import TabSwitcher from './TabSwitcher.js';
+
+export default function App() {
+ return (
+ {
+ return tabId[0].toUpperCase() + tabId.slice(1);
+ }}
+ renderContent={tabId => {
+ return
+
+ );
+}
+```
+
+
+
+A prop like `renderContent` is called a *render prop* because it is a prop that specifies how to render a piece of the user interface. However, there is nothing special about it: it is a regular prop which happens to be a function.
+
+Render props are functions, so you can pass information to them. For example, this `RowList` component passes the `id` and the `index` of each row to the `renderRow` render prop, which uses `index` to highlight even rows:
+
+
+
+```js
+import { RowList, Row } from './RowList.js';
+
+export default function App() {
+ return (
+ {
+ return (
+
+
+ );
+}
+```
+
+```css
+.RowList {
+ display: flex;
+ flex-direction: column;
+ border: 2px solid grey;
+ padding: 5px;
+}
+
+.RowListHeader {
+ padding-top: 5px;
+ font-size: 25px;
+ font-weight: bold;
+ text-align: center;
+}
+
+.Row {
+ border: 2px dashed black;
+ padding: 5px;
+ margin: 5px;
+}
+
+.RowHighlighted {
+ background: #ffa;
+}
+```
+
+
+
+This is another example of how parent and child components can cooperate without manipulating the children.
+
+---
+
+## Reference {/*reference*/}
+
+### `Children.count(children)` {/*children-count*/}
+
+Call `Children.count(children)` to count the number of children in the `children` data structure.
+
+```js RowList.js active
+import { Children } from 'react';
+
+function RowList({ children }) {
+ return (
+ <>
+
Total rows: {Children.count(children)}
+ ...
+
+ );
+}
+```
+
+[See more examples above.](#counting-children)
+
+#### Parameters {/*children-count-parameters*/}
+
+* `children`: The value of the [`children` prop](/learn/passing-props-to-a-component#passing-jsx-as-children) received by your component.
+
+#### Returns {/*children-count-returns*/}
+
+The number of nodes inside these `children`.
+
+#### Caveats {/*children-count-caveats*/}
+
+- Empty nodes (`null`, `undefined`, and Booleans), strings, numbers, and [React elements](/apis/react/createElement) count as individual nodes. Arrays don't count as individual nodes, but their children do. **The traversal does not go deeper than React elements:** they don't get rendered, and their children aren't traversed. [Fragments](/apis/react/Fragment) don't get traversed.
+
+---
+
+### `Children.forEach(children, fn, thisArg?)` {/*children-foreach*/}
+
+Call `Children.forEach(children, fn, thisArg?)` to run some code for each child in the `children` data structure.
+
+```js RowList.js active
+import { Children } from 'react';
+
+function SeparatorList({ children }) {
+ const result = [];
+ Children.forEach(children, (child, index) => {
+ result.push(child);
+ result.push();
+ });
+ // ...
+```
+
+[See more examples above.](#running-some-code-for-each-child)
+
+#### Parameters {/*children-foreach-parameters*/}
+
+* `children`: The value of the [`children` prop](/learn/passing-props-to-a-component#passing-jsx-as-children) received by your component.
+* `fn`: The function you want to run for each child, similar to the [array `forEach` method](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/forEach) callback. It will be called with the child as the first argument and its index as the second argument. The index starts at `0` and increments on each call.
+* **optional** `thisArg`: The [`this` value](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/this) with which the `fn` function should be called. If omitted, it's `undefined`.
+
+#### Returns {/*children-foreach-returns*/}
+
+`Children.forEach` returns `undefined`.
+
+#### Caveats {/*children-foreach-caveats*/}
+
+- Empty nodes (`null`, `undefined`, and Booleans), strings, numbers, and [React elements](/apis/react/createElement) count as individual nodes. Arrays don't count as individual nodes, but their children do. **The traversal does not go deeper than React elements:** they don't get rendered, and their children aren't traversed. [Fragments](/apis/react/Fragment) don't get traversed.
+
+---
+
+### `Children.map(children, fn, thisArg?)` {/*children-map*/}
+
+Call `Children.map(children, fn, thisArg?)` to map or transform each child in the `children` data structure.
+
+```js RowList.js active
+import { Children } from 'react';
+
+function RowList({ children }) {
+ return (
+
+ {Children.map(children, child =>
+
+ {child}
+
+ )}
+
+ );
+}
+```
+
+[See more examples above.](#transforming-children)
+
+#### Parameters {/*children-map-parameters*/}
+
+* `children`: The value of the [`children` prop](/learn/passing-props-to-a-component#passing-jsx-as-children) received by your component.
+* `fn`: The mapping function, similar to the [array `map` method](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/map) callback. It will be called with the child as the first argument and its index as the second argument. The index starts at `0` and increments on each call. You need to return a React node from this function. This may be an empty node (`null`, `undefined`, or a Boolean), a string, a number, a React element, or an array of other React nodes.
+* **optional** `thisArg`: The [`this` value](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/this) with which the `fn` function should be called. If omitted, it's `undefined`.
+
+#### Returns {/*children-map-returns*/}
+
+If `children` is `null` or `undefined`, returns the same value.
+
+Otherwise, returns a flat array consisting of the nodes you've returned from the `fn` function. The returned array will contain all nodes you returned except for `null` and `undefined`.
+
+#### Caveats {/*children-map-caveats*/}
+
+- Empty nodes (`null`, `undefined`, and Booleans), strings, numbers, and [React elements](/apis/react/createElement) count as individual nodes. Arrays don't count as individual nodes, but their children do. **The traversal does not go deeper than React elements:** they don't get rendered, and their children aren't traversed. [Fragments](/apis/react/Fragment) don't get traversed.
+
+- If you return an element or an array of elements with keys from `fn`, **the returned elements' keys will be automatically combined with the key of the corresponding original item from `children`.** When you return multiple elements from `fn` in an array, their keys only need to be unique locally amongst each other.
+
+---
+
+### `Children.only(children)` {/*children-only*/}
+
+
+Call `Children.only(children)` to assert that `children` represent a single React element.
+
+```js
+function Box({ children }) {
+ const element = Children.only(children);
+ // ...
+```
+
+#### Parameters {/*children-only-parameters*/}
+
+* `children`: The value of the [`children` prop](/learn/passing-props-to-a-component#passing-jsx-as-children) received by your component.
+
+#### Returns {/*children-only-returns*/}
+
+If `children` [is a valid element,](/apis/react/isValidElement) returns that element.
+
+Otherwise, throws an error.
+
+#### Caveats {/*children-only-caveats*/}
+
+- This method always **throws if you pass an array (such as the return value of `Children.map`) as `children`.** In other words, it enforces that `children` is a single React element, not that it's an array with a single element.
+
+---
+
+### `Children.toArray(children)` {/*children-toarray*/}
+
+Call `Children.toArray(children)` to create an array out of the `children` data structure.
+
+```js ReversedList.js active
+import { Children } from 'react';
+
+export default function ReversedList({ children }) {
+ const result = Children.toArray(children);
+ result.reverse();
+ // ...
+```
+
+#### Parameters {/*children-toarray-parameters*/}
+
+* `children`: The value of the [`children` prop](/learn/passing-props-to-a-component#passing-jsx-as-children) received by your component.
+
+#### Returns {/*children-toarray-returns*/}
+
+Returns a flat array of elements in `children`.
+
+#### Caveats {/*children-toarray-caveats*/}
+
+- Empty nodes (`null`, `undefined`, and Booleans) will be omitted in the returned array. **The returned elements' keys will be calculated from the original elements' keys and their level of nesting and position.** This ensures that flattening the array does not introduce changes in behavior.
+
+---
+
+## Troubleshooting {/*troubleshooting*/}
+
+### I pass a custom component, but the `Children` methods don't show its render result {/*i-pass-a-custom-component-but-the-children-methods-dont-show-its-render-result*/}
+
+Suppose you pass two children to `RowList` like this:
+
+```js
+
+
First item
+
+
+```
+
+If you do `Children.count(children)` inside `RowList`, you will get `2`. Even if `MoreRows` renders 10 different items, or if it returns `null`, `Children.count(children)` will still be `2`. From the `RowList`'s perspective, it only "sees" the JSX it has received. It does not "see" the internals of the `MoreRows` component.
+
+The limitation makes it hard to extract a component. This is why [alternatives](#alternatives) are preferred to using `Children`.
diff --git a/beta/src/sidebarReference.json b/beta/src/sidebarReference.json
index 24d467463..c7396afdd 100644
--- a/beta/src/sidebarReference.json
+++ b/beta/src/sidebarReference.json
@@ -13,8 +13,7 @@
"routes": [
{
"title": "Children",
- "path": "/apis/react/Children",
- "wip": true
+ "path": "/apis/react/Children"
},
{
"title": "cloneElement",