public function purge_children($requirefulltree) {
        $this->children = array();
        $this->fulltree = ($requirefulltree || $this->fulltree);
        $this->loaded   = false;
        //break circular dependencies - this helps PHP 5.2
        while($this->category_cache) {
            array_pop($this->category_cache);
        }
        $this->category_cache = array();
    }