forgetme.js

class Parent extends React.Component {
   constructor(...args) {
     super(args);
     this.state = {
       renderChild: true
     }
     
     this.interval = null;
   }
   
   componentDidMount() {
     this.interval = setTimeout(() => this.setState({renderChild: false}), 5000);
   }
   
   componentWillUnmount() {
     clearInterval(this.interval);
   }   
   
   render() {
     return (
       <div>
         { this.state.renderChild ? '<Child />' : null }
       </div>
     )
   }
 }