/**
  * Walk through each child and render it
  *
  * @param WP_Form $form
  * @return string
  */
 protected function render_children(WP_Form $form)
 {
     $children = '';
     foreach ($form->get_children() as $child) {
         $children .= $this->render_child($child);
     }
     return $children;
 }