I recommend that you fix it.
I was 14 when i got my first ever motorcycle, it was a 50 cc.derbi
http://p1.bikepics.com/pics/2004%5C1...62399-full.jpg
And the reason why we bought it was that it was broken/ didn't start. We tried all we could and finally the reason was reed valve, quick sandpapering and it worked well.
Then I rode it for couple hours and it was broken. This time we didn't even try to solve what was broken, but we opened up the engine and switched all new bearings and seals ( of course also piston and rod also). After that I've rode it for 8 thousand km. It was a great experience when we finally got it working (after changed almost all electrics) and I started riding it.
I've learned then (almost) everything I've needed so far on 2-stroke engine. And Gasser's maintaining is routine after doing that.
So, if you fix it, it will help your son to survive with possible problems with his Gasser.