I would start a kid with a 223, and feed it TSXs for deer and whatever that's cheap for LOTS of practice. Buy a 270 when they're big enough, and when they're ready. Bet they will be better shots in the long run, and will do more shooting with a gun that's actually comfortable to shoot.
No sense in running a kid away from shooting because the Dad was trying to be macho and make them shoot a "Man's Gun" before the kid is ready.
