The speech that worked (mostly) on the children in my life involved the concept of 'cannot unsee', which they seemed to understand. There are some parallels to gun safety here because there are things that even the adults in your life try not to do and it seems perfectly reasonable to expect the same from children.

In fact being held to a standard that adults hold themselves to is frequently seen as a rite of passage. I'm a big girl now and I put on my big girl pants to prove it.