WordPress: Dynamically shows first level child pages of a parent page without using a widget or menu.

_page.php

<?php 

global $post;

if(!$post->post_parent){
	$children = wp_list_pages("title_li=&child_of=".$post->ID."&echo=0");
	} else{
		if($post->ancestors) {
		//$ancestors = end($post->ancestors);
		$ancestors = end( get_post_ancestors($post) );
		$children = wp_list_pages("title_li=&child_of=".$ancestors."&echo=0");
		}
	}
	if ($children) {
	?>
	<aside id="child-pages" class="widget widget_child_pages">
		<ul> 
			<?php echo $children; ?>
		</ul>
	</aside>
<?php } ?>

<? //Placement: I usually place this code above the normal call for the sidebar ?>