code: def MultiListChildren(self, urns, limit=None, age=NEWEST_TIME):
      
      checked_subjects = set()
  
      for subject, values in data_store.DB.AFF4MultiFetchChildren(
          urns, timestamp=Factory.ParseAgeSpecification(age), limit=limit):
  
        checked_subjects.add(subject)
  
        subject_result = []
        for child, timestamp in values:
          urn = rdfvalue.RDFURN(subject).Add(child)
          urn.age = rdfvalue.RDFDatetime(timestamp)
          subject_result.append(urn)
  
        yield subject, subject_result
  
      for subject in set(urns) - checked_subjects:
        yield subject, []
docs: Lists bunch of directories efficiently.
  
      Args:
        urns: List of urns to list children.
        limit: Max number of children to list (NOTE: this is per urn).
        age: The age of the items to retrieve. Should be one of ALL_TIMES,
          NEWEST_TIME or a range.
  
      Yields:
         Tuples of Subjects and a list of children urns of a given subject.