I will repeat myself. Make sure it fits the child. If he is accurate with a 223 (and it's legal, it is here) then use a Barnes 50gr TTSX and go hunting. I know people that use a 22LR (no I won't say who or where) and they put it in the lungs. Deer walks 30ft, stands there for a few minutes and drops dead. My point is a well placed bullet will kill deer, period. If your grand kids can shoot a 243, even better.

In my opinion, there is no way I would let a kid shoot a rifle with a brake. A brake, to me, is only a way for someone to shoot something bigger than they should be shooting, that's just my opinion, and it applies only to civilian use.

The potential for hearing damage with a brake is phenomenal, and the damage is accumulative. They should be wearing hearing protection anyway, but a brake only points the blast back at the shooter, and others beside them. I have seen guys shoot big rifle with brakes, while hunting, only to blow debris in the eyes of people standing off to the side and behind the shooter. Sorry, but that is how I see it.

Use the lightest caliber possible, and a well designed bullet, and you will have a happy shooter. Having said all that, 8 or 9 IS pretty darned young to hunt deer.