Swearing is good for children.

Conventional wisdom has it that adults should not swear around children. That children themselves shouldn’t swear. Science says the opposite according to this article.
 
There’s a knee-jerk reaction that parents have to swearing, and you will feel it yourself if someone swears in the presence of your child. A strange defensiveness, a desire to protect them from the offending word, all tinged with the same regret we feel when something can’t be undone as much as we wish it could be.
 
This reaction is helpful while they are old enough to use language, but too young to understand how it makes people feel (empathy and cause and effect), and too young to have anything other than a fledgling self-control ability. This is normally between 2 – 6/7. Even at 5 they are only just developing the understanding that other people have thoughts. So while they may be able to predict where people will look for something they think they lost in a particular location, they are likely to still think a good present for mum is a toy they like. In fact, asking them what they think other people like is a good way for you to understand how developed their ability to anticipate others thoughts is.
 
But when they are 6 or 7, instead of creating a taboo around swearing, which just makes it more interesting, address it head on. Explain why people swear and how it can make others feel (uncomfortable, offended, hurt), and how it can make them appear to people (uncaring, rude, cool). Then it’s their choice. My eldest son (nearly 10) has his own no swearing policy because he doesn’t like the silliness that goes around it and the way swearing is done to impress peers. My youngest, 7, doesn’t have a policy, and although he tends not to swear, does enjoy the thrill of saying a rude word occasionally.
 
Here’s the science article.
 
And here’s an article by the brilliant Dave Trott about how he dealt with his children swearing.