If it's a pocket knife how are the cops going to see it? X-Ray vision? If they're using it, it's still none of a cops business, unless they're cutting someones throat or stabbing them. I've never heard of age restrictions on knives. Doesn't mean officer friendly wouldn't make something up on the spot to get an arrest, tho. Personally, I wouldn't worry about it.
Yep things sure has changed since way back when. When I went to school every guy carried a knife and nothing was wrong with that. It was the norm back then. But they were not going around threatening people wtht them either. The boys acted like they had some sense back then and also knew if they got in trouble at school it also meant being in trouble at home too. Lots of boys now do not have knives nor are they even allowed to be around them.
I think it is great that the OP is educating and exposing his kids to knives.
Good for you.