docs: def start_child_states(self, concurrency_history_item, do_not_start_state=None):
          """ Utility function to start all child states of the concurrency state.
  
          :param concurrency_history_item: each concurrent child branch gets an execution history stack of this
                                          concurrency history item
          :param do_not_start_state: optionally the id of a state can be passed, that must not be started (e.g. in the
                                      case of the barrier concurrency state the decider state)
          :return:
          """
          self.state_execution_status = StateExecutionStatus.EXECUTE_CHILDREN
          # actually the queue is not needed in the barrier concurrency case
          # to avoid code duplication both concurrency states have the same start child function
          concurrency_queue = queue.Queue(maxsize=0)  # infinite Queue size
  
          for index, state in enumerate(self.states.values()):
              if state is not do_not_start_state:
  
                  state.input_data = self.get_inputs_for_state(state)
                  state.output_data = self.create_output_dictionary_for_state(state)
                  state.concurrency_queue = concurrency_queue
                  state.concurrency_queue_id = index
  
                  state.generate_run_id()
                  if not self.backward_execution:
                      # care for the history items; this item is only for execution visualization
                      concurrency_history_item.execution_histories[index].push_call_history_item(
                          state, CallType.EXECUTE, self, state.input_data)
                  else:  # backward execution
                      last_history_item = concurrency_history_item.execution_histories[index].pop_last_item()
                      assert isinstance(last_history_item, ReturnItem)
                  state.start(concurrency_history_item.execution_histories[index], self.backward_execution, False)
  
          return concurrency_queue