I started my kids and grand kids on a sxs 20ga using very light hand loads at first to make sure recoil wasn't a problem for them. Also, chose to wait until they were large enough and strong enough to handle a 6 lb gun before moving to shotguns from .22s and .222 rifles. By the second season they were ready to handle the commercial 20ga light loads or my quail and dove loads of 3/4oz.

Because I learned on a H&R hammer single 16ga which weighed about 5lbs and the highest brass duck loads my dad could find it was well established recoil is a factor.