code: def ValidateChildren(self, problems):
      
      assert self._schedule, "Trip must be in a schedule to ValidateChildren"
      # TODO: validate distance values in stop times (if applicable)
  
      self.ValidateNoDuplicateStopSequences(problems)
      stoptimes = self.GetStopTimes(problems)
      stoptimes.sort(key=lambda x: x.stop_sequence)
      self.ValidateTripStartAndEndTimes(problems, stoptimes)
      self.ValidateStopTimesSequenceHasIncreasingTimeAndDistance(problems,
                                                                 stoptimes)
      self.ValidateShapeDistTraveledSmallerThanMaxShapeDistance(problems,
                                                                stoptimes)
      self.ValidateDistanceFromStopToShape(problems, stoptimes)
      self.ValidateFrequencies(problems)
docs: Validate StopTimes and headways of this trip.