Here you have the solution
<ul>
<?php
$children = wp_list_pages('title_li=&child_of=".$post->ID."&echo=0');
$subpages = ($post->post_parent) ? wp_list_pages('title_li=&child_of=".$post->post_parent."&echo=0') : wp_list_pages('title_li=&child_of=".$post->ID."&echo=0') ;
if ($children) { ?>
<li><?php echo $children; ?></li>
<?php } else { ?>
<?php echo $subpages; ?>
<?php } ?>
<?php wp_reset_query() ?>
</ul>
I used it to make a menu where the case was something like:
Parent Page: Service A
Child: Overview, Features, Service Plan, FAQs, Quotes
And there were different services and each parent has their own child.