code: def auto_generate_child_rel(self, klass, param):
          
          if self.down.t1 is not notpresent:
              self.t1_child_rel = ChildRelationship.create(
                  klass=klass, parent=self.t1, child=self.down.t1, param=param)
          if self.down.t2 is not notpresent:
              self.t2_child_rel = ChildRelationship.create(
                  klass=klass, parent=self.t2, child=self.down.t2, param=param)
docs: Auto-populate self.child_rel1 and self.child_rel2.
          This requires self.down to be another valid DiffLevel object.
          :param klass: A ChildRelationship subclass describing the kind of parent-child relationship,
                        e.g. DictRelationship.
          :param param: A ChildRelationship subclass-dependent parameter describing how to get from parent to child,
                        e.g. the key in a dict