一种方法是在foreach中创建另一个get\\u类别（$类别为$类别）

Example code

   //preparing an array to hold later info
    $grandchildren_ids = [];
    //getting the child categories of parent 72
    $args = array(
     \'orderby\' => \'name\',
     \'parent\' => 72,
     \'taxonomy\' => \'category\',
     \'hide_empty\' => 0
    );
    $categories =  get_categories($args);

    foreach ( $categories as $category ) {
    //setting up the args where the parents are the child categories
     $grandchildrenargs=array(
     \'parent\' => $category->term_id,
     \'taxonomy\' => \'category\',
     \'hide_empty\' => 0
     );
     $grandchildrencategories =  get_categories($grandchildrenargs);

      foreach ( $grandchildrencategories as $grandchildrencategory ) {
       //getting the grandchildren ids or whatever else is needed and populating the array
       $grandchildren_ids[] = $grandchildrencategory->term_id;
      }

     }
    var_dump($grandchildren_ids);