How do I modify this piece of code to make the #child_menu linger for a few seconds before it disappears?

Code:
$(document).ready(function() {
	$('#parent_menu').mouseover(function() {
		$('#child_menu').show();
	});
	
	$('#child_menu').mouseout(function() {
		$('#child_menu').hide();
	});
});
Thanks in advance.