Showing parent category, but not children.

Hi all,

trying to figure out how to do this. I have a parent category of featured items for the homepage. I only want to show items that are in the parent category *and* a child category. I have the structure like this as there is an archive page for the various children once they are no longer featured on the homepage. Structure is like this:

Homepage (Parent and ID4)
cat 1
cat 2
cat 3

<?php query_posts($query_string . '&cat=4' . '&orderby=rand' . 'showposts=6'); ?>

Thanks!