React Passing Data with Props

/components/Header.js

import React, {Component} from 'react';
import "./Header.css"

export class Header extends Component {

    render() {

        var classNames = "";

        if (this.props.isBold) {
            classNames += " bold";
        }

        return (
            <div className={classNames}>
                App
            </div>
        );
    }
}

Header.propTypes = {
    isBold: React.PropTypes.bool
};

/components/Content.js

import React, {Component} from 'react';
import "./Content.css"

export class Content extends Component {

    render() {

        var classNames = "";

        if (this.props.size === "small") {
            classNames += " small";
        }
        else if (this.props.size === "medium") {
            classNames += " medium";
        }
        else if (this.props.size === "large") {
            classNames += " large";
        }

        return (
            <div className={classNames}>
                {this.props.children}
            </div>
        );
    }
}

Content.propTypes = {
    size: React.PropTypes.string,
    children: React.PropTypes.array
};

App.js

import React, { Component } from 'react';
import {Header} from "./components/Header"
import {Content} from "./components/Content"


export default class App extends Component {
  render() {
    return (
      <div>
        <Header isBold={true} />
        <Content size={"large"}>
          Hello <i>World</i>
        </Content>
      </div>
    );
  }
}

References
https://github.com/mhdr/ReactJSSamples/tree/master/005