Given that DD1 doesn't know any 'bad words' at all yet AFAIK, would I regret taking her to Billy Elliot? A friend's in it and his 6yo's been twice, but then of course you would turn a blind eye if you were in it wouldn't you - I'd do the same rather than keep her away from a show her daddy was in.
I'm a bit of a swearer myself and it doesn't bother me but I gave it up (somehow) when I had kids and have no desire to hear 'language' coming from the DDs' mouths before I have to.