Having them liking shooting is a good thing, but I agree with not starting on a 22. Should start with a spring loaded bb gun, very low power & most are accurate enough at short range so they really start to desire & appreciate better accuracy and not to waste a bunch of shots. Then move them up to a non auto loading 22, whether it's a lever, pump or bolt action. Shotguns are the worst thing to start them with. Even a 410 has a lot of kick & blast compared to a BB gun & 22. They also teach them to just aim in the general direction & hope you hit something. Just like Carlos Hathcock when he was a kid used to bring home lots of small game to feed his family when he was a boy with his single shot 22. One Christmas he got a new shotgun & he was excited, but after 1/2 a day of using it & not being able to hit what he was aiming at, he went home & got his 22 single shot & never touched the shotgun again.This is also the reason I'm against starting children out on .22's. I know, I know, pluck the chickens and boil the tar.
A .22 is easy to fire. Absolutely no recoil, sound isn't deafening and the rounds come in boxes of 500. Usually, when a child is shooting a .22, you have to stop them. They can do it all day long, and now that they know how, do they really have to wait for you?
Start them out with a .410 or 20ga. (I prefer a youth model 20ga.) Even if its just mowing down grass or something similar, let them shoot until they say "I'm done!". And they will. They've experienced the recoil and the concussion, and when they are ready to walk away, you'll never have to worry about them getting and shooting it when you're not there. Then introduce them to .22's.