Real world pilots have strict limits on the amount of time they can fly and managing those hours effectively is part of a pilot’s and airline’s responsibilities.
As someone else pointed out, with a flight plan files and autopilot, there’s no need to be at the controls for a full transoceanic flight. I doubt a RW pilot would do it his or herself.
Perhaps you can set a weekly time limit and have your son responsible for managing those blocks himself — make it part of the challenge, as it were.