I'll cast another vote for the .243. If the kid is really bitten by the hunting bug, I am sure they will want other rifles as the years roll on-but the .243 will stil be useful to them, for varmint hunting, for the own kids and friends who begin hunting. If they don't become hard core hunters, the .243 is perfect for the occasional hunter-most of whom never shoot enough to handle much more recoil then the .243. I know if I don't get to the range for a month or two, the first trip finds me shooting my .243.
Will