index.jsx

const _fbBase = new Firebase('https://•••••••••.firebaseIO.com');

_fbBase.child('users/'+newUserID+'/conversations').on('value', function(snap){
  var obj = snap.val();
  var arr = Object.keys(obj).map(function (key) {return obj[key]}); // just converting to array - http://stackoverflow.com/a/26166303
  _this.setState({conversations: arr});
});

class ConvoList extends React.Component {

  constructor(props) {
    super(props);
  }
  
  onChildChanged(passedData) {
    // passedData here should be the clicked conversationID
  }

  // here I pass each indiviual conversation to the ConvoListItem component, but the ID probably gets lost
  render() {
    <div>
      {this.props.conversations.map((convo) => <ConvoListItem convo={convo} callbackParent={this.onChildChanged} />)}
    </div>;
  }
  
}

class ConvoListItem extends React.Component {

  constructor(props) {
    super(props);
    this.onClick = this.onClick.bind(this);
  }

  onClick() {
    // I need the conversationID here so that I can pass it up to parent
    this.props.callbackParent(conversationID);
  }


  render() {
    return <div className="convo-list-item" onClick={this.onClick}>
        <p>{this.props.convo.lastMessage}</p>
      </div>;
  }
}

// in render() method of Application class:
<ConvoList conversations={this.state.conversations} />