RE: 3.5yr old building 1st kit!!!!!
As long as the kid wants to participate, let him do all he can handle. He may surprise you and everyone you know.
He may also lose interest and that is when you need to let it rest. He has a lot of things to interest him before he gets hooked on any one thing.
Sounds like you have a good plan.
As long as he has interest you will both have fun and learn a lot
Good luck
Corsair Brotherhood #69