code: function(control) {
        return this._events.some(function (evt) {
           if (evt.eventType === "StartChildWorkflowExecutionInitiated") {
              if (evt.startChildWorkflowExecutionInitiatedEventAttributes.control === control) {
                 return true;
              }
           }
        });
     }
docs: lookup for StartChildWorkflowExecutionInitiated
  @param {String} control
  @returns {Boolean}