parent_component.js

class DumbosParent extends React.Component {
  state = { availableShoes: 6 };

  sellShoes = () => {
    this.setState(({ availableShoes }, props) => ({
      availableShoes: availableShoes > 1 && availableShoes - 1
    }));
  };

  render() {
    return (
      <div>
        <h1>I am Dumbos Father. I keep track of shoes.</h1>
        <p>available shoes: {this.state.availableShoes}</p>
        <button onClick={this.sellShoes}>Sell one pare of shoes</button>
        <Dumbo availableShoes={this.state.availableShoes} />
        <AnotherComponent availableShoes={this.state.availableShoes} />
      </div>
    );
  }
}