docs: def remove_children(self, id_):
          """Removes all childrenfrom an ``Id``.
  
          arg:    id (osid.id.Id): the ``Id`` of the node
          raise:  NotFound - an node identified by the given ``Id`` was
                  not found
          raise:  NullArgument - ``id`` is ``null``
          raise:  OperationFailed - unable to complete request
          raise:  PermissionDenied - authorization failure
          *compliance: mandatory -- This method must be implemented.*
  
          """
          results = self._rls.get_relationships_by_genus_type_for_source(id_, self._relationship_type)
          if results.available() == 0:
              raise errors.NotFound()
          for r in results:
              self._ras.delete_relationship(r.get_id())