function display_children($parent, $level) {
global $mdb2;
   // retrieve all children of $parent
   $query = 'SELECT cat_name,cat_id FROM categories 
   				WHERE cat_parent_id="' . $parent . '" ORDER BY cat_pos;';
	$subcats =& $mdb2->queryAll($query);
	if (PEAR::isError($subcats)) {
		$msg = 'Erreur survenue lors du chargement des preferences :' . $subcats->getMessage();
    	$this->my_die($msg);
	}
	print_r($subcats);
	if (!empty($subcats)) {
		foreach ($subcats as $key => $value) {
			echo 'here';
			return str_repeat('&nbsp;&nbsp;&nbsp;&nbsp;',$level) . $value['cat_name'] . "<br />" . display_children($value['cat_id'], $level+1);
		}
	}
}

foreach ($cats as $key => $value) {
	$content .= $value['cat_name'] . "<br />" . display_children($value['cat_id'],1);
}