List WordPress Child Pages in Parent Page

<?php if ( is_page() ) {
      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) {
   ?>
      <div class="sidebar">
<h2>Sub-pages of Current Page</h2>
<ul>
        <?php echo $children; ?>
        </ul>
      </div>
   <?php
} // End If Post
       } // End if is page
   ?>