As I stated in my last post, when youngsters reach 13 years of age, they are absorbed into the adult classes. If we had a large mid-teen group it might be different.
I taught this basic system with kids for about 25 years and it works really well. Curiously, here in the Tempe, AZ area most parents want their kids involved in something where they can "win trophies, etc). I have had several parents say, "why should I bring them if they can't get something out of it other than practice in the dojo?" It seems that trying to answer that question so that they understand is hopeless.
We have plenty of students who seem to understand though. They all have their own cars or ride bikes. Kids who have to depend on parents to bring them usually don't last long.