The .22LR would work for a head shot. Otherwise, I would try to stick with the lower recoiling guns for the youngsters. Unless you can get them out to the range and get them comfortable with the .30-06. What type of barrels do you have on the 20 gauge and the 410??? If they're rifled, you could use some sabot slugs. They are very accurate. If not, you could use rifled slugs but you'd probably want to get as close as possible to ensure a good clean shot. I don't recommend buckshot, but with a tight choke and engaging them up close, it'll work.