When my daughter was 7 she told us about a horrible word that was said that day at school. We braced ourselves and asked her which word it was. “The ‘S’ word.” she said hesitantly.
I thought I should discuss it with her, but just before I used the word myself, I asked her, “Which ‘S’ word dear.” She looked at me and said, “Stupid”. I smiled.
Now she is 15 and I think I've heard her say the real “S” word twice, but no other profanity. The "F" word or God's name in vain would result in some bad consequences for her.
Children learn curse words from their parents mainly, until they are older. My father was extremely profane on a regular basis and I picked up the habit. When I was in high-school I began trying to clean up my act and by the time I was in college I rarely if ever cursed. I have my own personal standard of allowing the very rare crude word (dealing with excrement), but not other words that I consider profane or vulgar.
I did not hear any profanity until I was 11 or so. But I didn’t dare to use it at home! Blasphemy on the other hand, I picked up when I was maybe 3 from listening to our neighbor rant at the TV. He was pathologically incapable of forming a sentence without inserting a “GD” or a “JC”. A very sound spanking cured me for life.
My father was the same way, an old WW II vet and career military man, he could let out a string of profanity that would make a bartender blush. I remember him to this day working on the old car with a Cigarette hanging out of his mouth, cussing to high heavens. I've been told that shortly after I learned to talk I could imitate one of his profane rants to a "t". He thought it was hilarious...until I started doing it out in public... I guess between that and mom's complaining, it finally convinced him to stop cussing...or at least try to keep it PG rated, which he was pretty good at, unless he was really angry.