I am sure we could debate this all day long and everyone has there way.
In my view a muzzle loader just does not have the Kinetic energy that a 243 has. The idea with young hunters is to have them successfull right out of the gate. I think a scoped 243 or even a 257 Roberts can do the trick. Time on the range is most important but with the knockdown power a centerfire cartridge carrys will make the kill quick and clean. There is more room for marginal shots with a muzzle loader then a centerfire rifle. I know several kids who were very succesfull this last fall shooting 243's.
I knew plenty of "old timers" that shot 223's but the kill shot was the head, not the shot you want to teach a youngster.
Just my 2 cents!
Either way getting the youngsters involved is the way to go!!!