Check page for child pages

Hey guys,

I have a site where I have some pages who have subpages. I need to list those subpages and the parent page. I want to do this conditionally so that the parent page doesn’t get list on a page without children.

Here is my code:

function has_children($post_id) {
    $children = get_pages("child_of=$post_id");
    if( count( $children ) != 0 ) { return true; } // Has Children
    else { return false; } // No children
}

add_action ('genesis_before_post_title', 'subpage_nav');
	function subpage_nav(){

		if ( has_children($post->ID) ) {

		echo '<div id="pagenav">' . '<ul class="clearfix">';
		wp_list_pages( array('title_li'=>'','include'=>get_post_top_ancestor_id()) );
		wp_list_pages( array('title_li'=>'','depth'=>1,'child_of'=>get_post_top_ancestor_id()) );
		echo '</ul>' . '</div>';
	   }

   else;

	};

This is listing the parent and child page. What am I doing wrong.

Thank you,
Keith