Sort “get_pages” by menu order not ordering

I’m using this bit of code to generate a page full of items but they won’t sort into the menu order, any ideas as to why?

   <?php $pages = get_pages(array('child_of', 'menu_order')); ?> 

It should look like this:

<?php
$pages = get_pages( array('sort_column' => 'menu_order') );
?>