I'll jump in for a second.
With ANY class structure, some bikes will be more competitive than others. Allowing certain bikes certain modifications becomes complex. I don't want to see protests in the Jr Motard class!
The idea is to get their feet wet and have them ready for the Formula 7 class when they are old enough in fact, some of the jr motard riders are old enough for F7). With a year or two of Jr Motard, they won't be as shocked when they are on the track with faster bikes.
I am in the same place as you, my boys PW50 isn't going to be competitive against a PW80.
There are options, but I don't think they fit with the spirit of the class. The original draft of the class was actually a spec class with only one machine allowed.
I have one thing I am working on, I am discussing it with the BoD.