Here's the FF compromise between exploiting your children and not making them "juniors":

Give them a different first name with the same initial as your first name. Then buy their tickets as "J Duxfan" instead of "Junior Duxfan" and submit them for mileage credit after the flight.

Downside: you won't be able to buy their tickets with a youth or child discount.

Bear in mind that this violates the rules of probably every FF program and if you are caught you will lose all your mileage.

I think the solution of crankyusi was to fly with his children so that he and they all became United 1K flyers, with the corresponding 6 systemwide upgrades each that he can use on other travel. That's honest, and I like it better philosophically.

OTOH I do confess that once or twice, long before I became a member of the bar, I flew under the name of Law Lord Sr. so that he could retain his Premier status.