code: def get_child_books(self, book_id):
          
          # Implemented from template for
          # osid.resource.BinHierarchySession.get_child_bins
          if self._catalog_session is not None:
              return self._catalog_session.get_child_catalogs(catalog_id=book_id)
          return BookLookupSession(
              self._proxy,
              self._runtime).get_books_by_ids(
                  list(self.get_child_book_ids(book_id)))
docs: Gets the child books of the given ``id``.
  
          arg:    book_id (osid.id.Id): the ``Id`` of the ``Book`` to
                  query
          return: (osid.commenting.BookList) - the child books of the
                  ``id``
          raise:  NotFound - a ``Book`` identified by ``Id is`` not found
          raise:  NullArgument - ``book_id`` is ``null``
          raise:  OperationFailed - unable to complete request
          raise:  PermissionDenied - authorization failure
          *compliance: mandatory -- This method must be implemented.*