My friend olddrum1 hit it perfectly: "Keep it fun for them."
If a kid is being hurt by recoil, or is fearful of the recoil, he's not going to be having fun. I recall an incident when a father was forcing his two young sons to shoot a round of Skeet. After Station 1, the younger one (quite small) had had enough. At Station 2, he was crying and having tantrum, and the older one wasn't a happy camper, either; but, the father made them continue shooting. I suspect neither youngster will ever want to shoot again.