code: def children(self, table_name, primary=None):
          
          return dict(p[1:3] for p in self.out_edges(table_name, data=True)
                      if primary is None or p[2]['primary'] == primary)
docs: :param table_name: `schema`.`table`
          :param primary: if None, then all children are returned. If True, then only foreign keys composed of
              primary key attributes are considered.  If False, the only foreign keys including at least one non-primary
              attribute are considered.
          :return: dict of tables referencing the table through foreign keys