This conversation makes me curious what the legal definition of "use" is. If a parent/guardian purchases a motor, but the minor puts it into the rocket, then who is the user in this case? What if the kid only does the countdown and presses the launch controller button?
I am no expert, but it seems to me that if the parent does all the handling of the actual motor itself, then it's kind of a question of interpretation of who's actually "flying" the rocket. If a really skilled 12-year-old builds a rocket, and it's solidly built - say, examined by an RSO at a club launch or whatever, but then his or her parents actually set it up and launch the thing, to me, it seems like the kid is getting all the benefits of seeing a rocket he built fly, without breaking any rules. I am not up to HPR yet, but with my rockets, the fact that I built them is often enough for me. I don't necessarily have to be the one to press the button.