public function get_children($id)
 {
     $categories = array($id);
     $docwatch_category = new docwatch_category($id);
     $children = $docwatch_category->get_children();
     foreach ($children as $child) {
         $categories[] = $child;
         $categories = array_merge($categories, $this->get_children($child));
     }
     return $categories;
 }