My kids don't curse.
I am very pleased to be able to say this. It's not that they don't know bad words, it's not that they don't occasionally say something they shouldn't in a moment of anger, but in general they don't curse.
We've made it clear that there are words which are inappropriate to use, but we've never made that big a deal of it.
Pippi tells me that there are kids in her school who can't seem to have a conversation without using a hundred curses. The "f" word is a popular adjective I suppose. So, even though one would think she would be a little numb to bad words, when we were reading Shakespeare together and the quoted text she had to read said "Hell", she blushed and changed it to "heck."
One time Harry was upset about something (I don't remember what) and he looked at me and asked "Can I curse?" And I said yes. "Just this once." Because I know that sometimes when something really has you upset, it can kind of help to say something really bad. He looked shocked at my answer and then, real softly said (and I quote) "d word". Even given permission, he couldn't bring himself to actually say something bad (I was very proud.)
Lately though Harry has taken to "beeping". You know, pretending to curse but "beeping" himself out. So his sentences are littered with censored curses. But when I (after getting tired of constant beeping) told him that even though he wasn't saying the word, he was thinking about cursing, and he should try not to do that either, and he stopped.
Let's hope they keep this up!