Hi there, 6.5x55, 7mm-08 are excellent calibres for your needs, However,
if your son is only 10 years old, i'd suggest going the .243, 260 rem or 6mmbr, and shoot the lightest range of bullets until he gets confident with the centre fires,
when he can call the shot, increase the loading or bullet weight until you get into the hunting rounds weight range, 95 to 105 grains,
too much gun too quickly will give him anticipition of recoil, and so fluff the shots, once this is inbuilt into a young person its very hard to get rid of it,
dry firing procedures have to be then m