Since he is 9 and will eventually outgrow the bike, and since you mentioned cable and pedal brakes, I would suggest a "transition bike"... one that has a hand/cable front brake and either just a coaster (foot) brake or coaster plus hand rear brake.
Eschew Roadmaster, Hyper, and most x-mart bikes like the plague... they aren't well made or put together with care.
Personally, Bob, I would let him "abuse" a used bike till he learns to care for his machine. That I would deem practical. Even better, if there is a bicycle co-op nearby, the two of you could build him the bike of his dreams and he would learn maintenance (with Granddad!) at a wonderful, young age....
For me, it has been 6 years of a used Trek that I still ride and have no wish to replace.