.243, I taught a 9 yr. old boy to hunt (the son of a widowed friend) with a .243 and he took, over several years, 4 very good mule deer bucks, two pronghorn antelope and a ram with it. This kid was afraid of his own shadow and very timid. IMO Trigger control must be consistently drilled into their impressionable young minds. It is a mind over matter thing, sight picture and trigger control no other thought or fear. At first all young kids will think "will it kick me". .25-06 is another option. Good Luck!

i use a .243 this last sunday i took a 7 pt. buck at 168 and drooped him in his tracks. I own a .223 and the .243 the .243 is a better gun for someone who has never shot a deer its a gun that i started off with the kick will not hurt just put a good recoil pad on it and he will be good to go!