page list of children of level 2

function grandchild_level_list_pages() {
global $post;
$pages_tree = array_reverse(get_post_ancestors($post->ID));
$pages_tree = array_merge($pages_tree, array($post->ID));
if(is_page() && $pages_tree[1]) :
$this_page = $pages_tree[1];
// a condition that shows this list in the ancestry of the current page
$plist = wp_list_pages('title_li=&child_of=' . $this_page .'&depth=1&echo=0');
if(plist) { ?>

<ul class="menu layer-grandchild">
<?php echo $plist; ?>
</ul>

<?php }
endif; //end if($pages_tree[1])
}