Fluxo de componentes pai > filho

App.js

import React, { Component } from 'react'

class Filho extends Component {
  render() {
    const onClick = this.props.onClick
    return (
      <div>
        <button onClick={() => onClick()}>
          Click me!
        </button>
      </div>
    )
  }
}

class Pai extends Component {
  constructor(props) {
    super(props)

    this.state = {
      count: 0
    }
  }

  incrementCount() {
    this.setState({
      count: this.state.count + 1
    })
  }

  render() {
    return(
      <div>
        <h1> Contadot: { this.state.count }</h1 >
        <Filho onClick={this.incrementCount.bind(this)} />
      </div>
      )
  }
}