I don't know anything about the legalities of buying points for youngsters, but if it is legal I would sure encourage you to do it for them.
A quick search of the state(s) regs you are interested in should answer your questions, and provide more reliable information. When it comes to legal questions it is always best to go directly to the source. It's just a guess, but I would think that the youth would probably need to be old enough to qualify to buy a hunting license. What is the minimum age to hunt in WY?