need span in $cildren parameters.

I have a theme that I need help with writing out code for the children “sub nav” menu.

Here is the php

<?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 } ?>

I need to know what it should be in php if it looks like this in html

<div id="mid">

		<div id="mid-inner">
        <ul>
        <li><a href="#"><span>Home</span></a></li>
        </ul>
			<div id="search">

			</div>
		</div>
	</div>

* Please notice that there is a <span> in between the link name!

Thanks,
Adam