That is the beauty of the black powder rifles. They can be down loaded for just this kind of event. Our group often times brought the kids up to the cabin where we shot black powder rifles, told lies, rode ATV's and had a cookout. Since the kinds wanted to shoot we would load the Hawkins and Renegades down to 50 grains of powder and a patched roundball. Because of the weight of the rifle, recoil is next to nothing. We had some pretty young boys shooting our rifles and they are now all hooked. We'd set them in a chair and bench rest the rifle off the front rail of the cabin and let them shoot...
Load the rifle with 50 grains and a patched roundball and try it yourself. You will see there is little recoil and the accuracy of that load will surprise you. These rifles loaded light make a great small game rifle if your a good shot, and the young people really like all the smoke and noise.
We always held the rifle out in our hands and showed the timid ones we could pull the trigger making the gun fire and that there was no recoil. After they saw that the only hard part was getting in line to shoot with them. The best part is after they have shot a few rounds off you can mention that the load they just shot was strong enough to take a deer at moderate ranges... That always makes them smile..