I might be sticking my head out so everyone please feel free to stomp on it if you feel justified.
If I were you Jason, get a decent crossbow your kid can grow into and have a great experience with. The great experience would be to not wound a deer because of substandard equipment and not be frustrated because of a very limited range. That being said I think if you have a bow/kid combination that can consistantly put a good broadhead into a two inch circle at 15 yards then you should be ok. Use a broadhead like a Wensel Woodsman or a Snuffer and keep inside of 15 yards and I doubt these two broadheads will do anything but pass through a deer.
Ok boys let me have it!