My friend has a 9 year old that shoots the new Ruger compact rifle in 260. He weighs about 60 lbs. On the other hand the 243 will kick less and is capable of taking deer out beyond 150 yards. However, with the 243 shot placement is very important. I guess really shot placement is important with all big game rounds though. Either caliber is capable but I would go with the 260. As your child grows he will out grow the 243 and the 260 has better power if he tries to tackle other big game. If you go with the 243 in the ADL to save money they do have a youth model in the ADL. There are a number of other rifles for the small hunter including Browning, Winchester, & Ruger. The Ruger compact is very light and easy to handle. Also, if you end up with the 243 shoot the Federal Premium 100 gr. Nosler Partition. This is the load I started with at age eleven. The NP will hold together well and provide plenty of penetration on deer for the 243. Good luck in choosing a firearm for you child.