sdsno, I hope he's recovered fully.
Our's, 6 and 10 (today) have been around sleds, getting pulled in the sno coach or riding squirrel since they were infants.
Started letting them "drive" with me holding the bars at about 5 y/o.
They don't have dirtbikes or quads, but do ride them fairly frequently the last year or 2.
The older one took his first solo ride last winter on the ole 440. Ended up being a very long trip due to new area and we missed a turn back to the truck combined with an avg speed of about 8 mph!
I can see how they are progressing much better this year, but lapses in basic "traffic awareness" get the 10 y/o scolded regularly. He is good about staying to the right, but looking both ways at intersections is lacking.
I generally keep him in front of me unless I need to go rip it up for a min to cool my sled down, but mom is still behind him then.
Yes, it's risky but so is letting them walk to the bus stop.
The 6 y/o got to pilot the first time by himself this year for an entire afternoon out on a lake. Surprised me how well he did, but then he also tried to do a "whip", his favorite X games trick off a jump on the shore of the lake!
Haha, sled booted him off and he gained some respect there in a pretty safe environment.
Bottom line it's all about the ability and maturity of the kid AND supervision.
I wrapped my old sleds up quite a few times between the ages of 10 and 13 (even happens now!). Guess I don't see it being much more dangerous than skiing or contact sports if the kid knows not to out ride his/her ability.
Difference is, I was almost never supervised as we did not own sleds as a family, I bought one on my own at 10 years old.
The biggest worry for me is this is not IL where I grew up riding where the 3 biggest hazards were trees, fences and culverts. Here my kid is riding 80% of the time on a trail that if he effs up he could end up going over the edge.