How to add additional props to a React element passed in as a prop?

Pass in the component constructor instead of an instance:

class Menu extends React.Component {
    render() {
        return(
            <div className="Menu">
                <MenuItem icon={MdInbox} />
                <MenuItem icon={MdDrafts} />
                <MenuItem icon={MdTrash} />
            </div>
        );
    }
}

The child class:

class MenuItem extends React.Component {
    render() {
        // This constant must begin with a capital,
        // it’s how React distinguishes HTML elements from components.
        const Icon = this.props.icon;
        return(
            <div className="MenuItem">
                <Icon size={24} />
            </div>
        );
    }
}