code: public void removeChildAt(int index) throws IndexOutOfBoundsException {
          Node<T> child = children.get(index);
          child.parent = null;
          children.remove(index);
      }
docs: Remove the Node<T> element at index index of the List<Node<T>>.
  @param index the index of the element to delete.
  @throws IndexOutOfBoundsException if thrown.