Which muscles do you use to hold your bladder?

I have a friend who says she doesn’t want to have kids because the women in her family have a tendency to loose control of their bladder after having children. (Just when sneezes or coughs arise)

I haven’t had this problem but I… uh…do my excercises.

So I was wondering if that could be a solution to her problem, or if there was more to loosing bladder control after having a child.