// @flow 
import React from 'react'

type PropsA = {
  children?: React.Node
}

const A = (props: PropsA) => (
  <div>
    {props.children}
  </div>
)

const ComponentA = () => <A>Test</A>

type PropsB = {
  children: React.Element<any>
}

const B = (props: PropsB) => (
  <div>
    {props.children}
  </div>
)

const ComponentB1 = () => <B/>                     // error
const ComponentB2 = () => <B>text</B>              // error
const ComponentB3 = () => <B><span>text</span></B> // works!
const ComponentB4 = () => <B><span>foo</span><span>bar</span></B> // error