How do you stop your child swearing when they don't know what they're saying?

I'll admit it, it's pretty funny when little kids swear and they don't realise what they're saying. But it might not be as funny to the people around them if it happens out in public! So should you just ignore it or pull them up? Especially if they don't realise what they're saying.   See omnystudio.com/listener for privacy information.