render() {
  const children = React.Children.map(this.props.children, (child, index) => {
    if (child.type === Panels) {
      return React.cloneElement(child, {
        activeIndex: this.state.activeIndex
      });
    } else if (child.type === List) {
      return React.cloneElement(child, {
        activeIndex: this.state.activeIndex,
        onActivateTab: activeIndex => {
          this.setState({ activeIndex });
        }
      });
    }
    return child;
  });

  return <Fragment>{children}</Fragment>;
}