[petercooper]

I suspect he is quite familiar with all the swear words yet behaves himself in public so all is well.

Yeah, I think it depends on the kid and the parents' ability to define boundaries and not treat kids as mini-adults with the rights of adults. My dad swore like a trooper (still does) and I knew all the words by the time I was a teenager, but I didn't dare swear until I was an adult.

It's decidedly untrendy to treat kids as kids and adults as adults these days, but I think having one rule for kids and one for adults is the best way to go.