Feel for your son, but mountain or even flat land riding comes with many risks..
I remember when I was 9 and my John deer spit fire throttle got stuck and I went into the cultivator, then when I was chasing a cycote and broke a front ski, nose diving into the hard dirt snow, also hit a few gas well roads that got plowed, flew like a ragged dall
He's 15 and it's a belt, if he stays in the sport I can promise him many more stupid crap happening over his years sledding, no ones fault, just sh1t happens
Just this last weekend I flew over the hood a couple times in poor Revy vis.. Month before broke a rib on a branch.. But all in all, do your best to teach him general common sense safety and he will pick up the rest..
Broke many belts, and flew over many hoods, keep teather on and hope and pray that my reeds did not blow out as I'm waking back in a daze..
We have the best sport out there, but it comes with some risk..