All down to their parenting I am afraid.
Weak parents and the kids grow up doing all sorts and swearing.

I am proud that my 2 children have grown without any problems like that.
Mind it did take a bar of soap one New Years Eve for my boy to realise that he was not allowed to swear.
To this day he still will not swear in front of me.Yes I know there will be times when he as to let off a little steam but as long as I am not around it doesn't bother me. Has for swearing in public well he as the kind of job that he really cannot use those words.

Has for my daughter oh no she never swore she was and is an angel. She was a teacher so she was again in a job where she could not use those words but now she is working in the Science Museum and mixing with youngster degenerates I have noticed a few choice words on her FB page that she as shared.
I just pm her and say "tut tut Ellie.".