public function add_child( $item ) {
		if ( !$this->has_child_class ) {
			$this->add_class('menu-item-has-children');
			$this->has_child_class = true;
		}
		$this->children[] = $item;
		$item->level = $this->level + 1;
		if ( count($this->children) ) {
			$this->update_child_levels();
		}
	}