Welcome to The High Road, Eric.
Reactive targets are always a great inclusion for anyone, and kids tend to like em even more than the rest of us. I haven't crossed the bridge you're at, as my only kid is two years old.
but I can tell you what made
me enjoy shooting so much.
My brother and I are a couple years apart, and we started shooting together at ages 6 and 8. Our targets were usually empty aluminum cans, which we always enjoys knocking down, denting, etc. At some point after we progressed to shooting our pellet guns unsupervised, we decided to start shooting our little green plastic/molded army men - the kind that come a few dozen to a bucket for $4-5. We set em up on long mounds of dirt and got in the prone, and pretended we were "at war." The bonus was the army men were surprisingly reactive, and pretty difficult targets, even at as little as ten yards.
Some people are firmly against letting their kids even point toy guns at each other, so I assume they wouldn't let their kids even shoot at toys shaped like people. If that's you, that's fine. The point is, try to think like a kid. Sometimes shooting is even more interesting if you combine it with something else (like our "war" games). If they're competitive, come up with some varied events for them. An episode or two of Top Shot might give you some ideas you can adjust for at home.
Hope this helps you out a bit.