Imprimir os sub menus apenas das categorias em questão.

Loop sub menu

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

OR

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