Between the ages of one and two, in fact, Jay's experiments showed that boys drew on a vocabulary of six such words; girls eight. This expanded rapidly, with five to six-year-old boys using 34 words, and girls of the same age 21, the Guardian reported.
Parents tend to want to protect children from swearwords. We've probably all experienced the awkwardness of swearing in front of the children of friends we forgot were there.
But Jay's study suggests the impulse is futile, at least if we believe it'll stop them learning the words at all. What it might do, however, is teach them about context.
There's a time and a place for swearing, and a sense of taboo can help children understand that society expects different standards of behaviour in different surroundings.