Page List Thumbnails

Hi, I use the following code on a page to show a list of child pages:

<?php
		$children = wp_list_pages('title_li=&depth=1&child_of='.$post->ID.'&echo=0');
		  if ($children) { ?>
		  <ul class="subpage-list">
		  <?php echo $children; ?>
		  </ul>
<?php } ?>

How can I also show the thumbnail for each page in the list?