code: def child(self, logger, action_type, serializers=None):
          
          newLevel = self._nextTaskLevel()
          return self.__class__(
              logger, self._identification[TASK_UUID_FIELD], newLevel,
              action_type, serializers)
docs: Create a child L{Action}.
  
          Rather than calling this directly, you can use L{start_action} to
          create child L{Action} using the execution context.
  
          @param logger: The L{eliot.ILogger} to which to write
              messages.
  
          @param action_type: The type of this action,
              e.g. C{"yourapp:subsystem:dosomething"}.
  
          @param serializers: Either a L{eliot._validation._ActionSerializers}
              instance or C{None}. In the latter case no validation or
              serialization will be done for messages generated by the
              L{Action}.