react.dev/cookbook/cb-07-children-prop-type.md

id	title	layout	permalink
children-prop-type	Type of the children prop	docs	children-prop-type.html

Problem

You get errors while manipulating this.props.children inside a component.

Solution

Usually, children is an array of components. To save an extra array allocation, when it only contains one single component, it returns the component itself.

This means accessing, for example, this.props.children.length might be misleading since it could be the length property of a single string component.