Sidebar Navigation with Subpage and Parent menu

post_parent)
$children = wp_list_pages(‘title_li=&child_of=’.$post->post_parent.’&echo=0′); else
$children = wp_list_pages(‘title_li=&child_of=’.$post->ID.’&echo=0′);
if ($children) { ?>

post_parent);
echo $parent_title;
?>