Ever since the first humans started drawing in caves, there were some cavemen who drew dodgy pictures. The pyramids probably have some secret chamber of inappropriate hieroglyphics and when the Romans started building walls, people started writing explicit things on them.
Not everyone uses their creative potential to draw or write dodgy content and then share it with others in public places; but for some reason, there has always been a bunch of humans who have found drawing specific things on someone else’s pencil case very amusing. However, not everyone wants to see the dodgy stuff that these dodgy people are creating. So how do you help your kids to navigate a world with a small group of dodgy people, who get a kick out of creating dodgy stuff and putting it where other people can see it?