<?php
if($post->post_parent)
$children = wp_list_pages("sort_column=menu_order&title_li=&child_of=".$post->post_parent."&echo=0");
else
$children = wp_list_pages("sort_column=menu_order&title_li=&child_of=".$post->ID."&echo=0");
if ($children) { ?>
<ul>
<?php echo $children; ?>
</ul>
<?php } ?>

Display parent headline and a list of children links in a submenu.

In this illustrative example:

• Services is the parent
• Service 1, Service 2, and Service 3 is children

The headline in the left column is Services both on parent as well as children page.

And this is the code:

<h2><?php
$parent_title = get_the_title($post->post_parent);
echo $parent_title;
?></h2>
<?php
if($post->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) { ?>
<ul>
<?php echo $children; ?>
</ul>
<?php } ?>