Let me start off by saying that it is terrible when something like this happens. The same kind of accident killed a young girl on a few blocks from me in Jersey this past July.
With that said though, am I the only who can't figure out for the life of me WHY you wouldnt just jump the hell off?? I know everything happens very quickly, but if you are a carrying enough speed to kill or seriously injure yourself towards a dock, you have to have at least a few seconds to realize things are about to go real real bad.
Personally, I think that boating laws should operate like the IJSBA. Younger kids should be able to ride, but let em ride a stand-up with some sort of permit obtained through a safety. And im not talkin about the B.S. classroom course the Coast Guard Auxiliary conducts, I mean like an on water safety course. The same should apply to couch riders, but I think you should be at least 17 or so to operate a couch alone.