Wordpress Temples: This creates a conditional based on the parent page ID. If ( specific page || checks for existence of having our parent page || looks for all ancestors of our parent and limits it to those children only ) The query brings back posts that are children of our parent.

Wordpress Templates

<?php
//Set up the variables of the parent page ID's
$parentPageID = '509';
?>
<?php if (is_page($parentPageID) || $post->post_parent == $parentPageID || ($post->ancestors && in_array($parentPageID, $post->ancestors) )) { ?>
    <h3>Child Pages</h3>
    <ul>
	<?php
	//Queries for all pages that are children of our parent ID
	?>
	<?php
	query_posts(array('showposts' => 5, 'post_parent' => $parentPageID, 'post_type' => 'page'));
	while (have_posts()) {
	    the_post();
	    ?>
	    <li><a href="<?php the_permalink() ?>"><?php the_title() ?></a></li>
	<?php } ?>
    <?php wp_reset_query(); ?>
    </ul>
<?php } ?>