WP Grandchildren

gistfile1.txt

the_post();
$children = new WP_Query( array('post_type' => 'page', 'post_parent' => get_the_ID() );
$ids = array();
if ($children->have_posts()) {
  while ($children->have_posts()) {
  $children->the_post();
    array_push($ids, get_the_id());
  }
}

foreach ($ids as $id) {
  $grandchildren = new WP_Query( array('post_type' => 'page', 'post_parent' => $id );
  while ($grandchildren->have_posts()) {
    $grandchildren->the_post();
    the_title();
  }
}