If I swear it's usually when I'm very angry
Although, there is something I once read: Those who swear a lot show just how low there IQ is, while those who swear around children show just how much they care about those around them.
I don't curse around children, espically my brothers son (who is only seven years old) normally when I get rather angry, and if he's around, I'll get out of the house and walk around the block for a little bit
Either way, and even I say this, there truly isn't any reason TO curse, around children or anyone else