If the parents were to sue I would see that being both a justice and an injustice.
It's BS that the father would sue because his child dead due to his own negligence. He allowed the child to operate the vessel therefore he is just as responsible for the childs death as anyone else and suing really isn't just.
However, if the father does sue and manages to win there is going to be a hail storm of law suits over the next couple of years that will result in a lot changes. Changes for the better. Ultimately the jet ski rental business will fold due to no longer being able to obtain affordable insurance or they will make changes so that uneducated people can not and will not get their hands on PWC's. That IMO would be a great justice.