getChildCids example

\Drupal::lock()->release($this->threadLock);
      $this->threadLock = '';
    }
  }

  /** * {@inheritdoc} */
  public static function postDelete(EntityStorageInterface $storage, array $entities) {
    parent::postDelete($storage, $entities);

    $child_cids = $storage->getChildCids($entities);
    $comment_storage = \Drupal::entityTypeManager()->getStorage('comment');
    $comments = $comment_storage->loadMultiple($child_cids);
    $comment_storage->delete($comments);

    foreach ($entities as $entity) {
      \Drupal::service('comment.statistics')->update($entity);
    }
  }

  /** * {@inheritdoc} */