Years ago when my kids were small, too small to crank a break action springer (and I got tired of doing it for them) I came up with a way to keep them shooting in the basement. I had a TC Carbine with youth stock and a 223 barrel. I primed a bunch of cases with small pistol primers, dropped a .22 pellet into the chamber, poked it just a bit with a piece of cleaning rod to make sure it went straight in, and loaded the primed case behind it. The kids were used to shooting this rig out of doors, so the familiarity factor was in our favor. (I still had to cock the hammer for the little one (5 yrs), though the older one (10) could do it herself about half the time)
It worked great, and was very quiet. It also turned out to be a way to show the kids how they would sometimes flinch when shooting it with the centerfire barrel. It proved to me, and them, that a lot of the flinch was related to the noise of the .223, since recoil was minimal.
Anyway all went well until one day, the (now ex) wife hollered down the stairs "Are you shooting a real gun in the basement?" It turns out she couldn't hear us, but after awhile she could smell the results of the primers going off. She was alright with an airgun going off at 500-600 fps, but didn't like the "real" gun shooting pellets at around 300 or so. (I did chrono them)
Fortunately we had already managed several evenings with it when she hadn't been home (and we continued afterward when she went out). The kids learned a lot about sight picture, breathing, squeezing (that TC had a great trigger compared to the airguns we had). Nowadays, 10 years later, they can whup me more often than not when we have a family fun match, air rifle or "real" one.
I can still outdo them both with a Ruger 357 Blackhawk though, but they are nipping at my heels there too!
Cheers
Kerry