...censor your kid when they start calling people snot-eating bastards...
That really doesn't sound like something a child should be censored for saying. It might give them the impression that profanity is somehow wrong, or inappropriate. That's not the message that we should be putting out.
We should encourage kids to be creative and enthusiastic with profanity, and to express themselves in unique ways. The only time they should be censored is when they're spouting the same old tired shit as every other child, over and over again.
That's when it's time to sit them down for a few hours with Roger's Profanisaurus.