code: def get_children(self):
          
          if self.is_leaf():
              return get_result_class(self.__class__).objects.none()
          return get_result_class(self.__class__).objects.filter(
              depth=self.depth + 1,
              path__range=self._get_children_path_interval(self.path)
          ).order_by(
              'path'
          )
docs: :returns: A queryset of all the node's children