My son has a mossberg bantam 20-gauge and killed his first turkey with it when he was 8 (he'll be 10 in March). I had him shoot it with 2 3/4" shells and when it came time to hunt put 3" shells in it (I patterned it with those when he wasn't home). Anyway he never knew the difference and still doesn't.
" Some localities are willing to work for their sport, and have plenty. Others are willing merely to take what comes easy, and have little or none." - Aldo Leopold