A while ago, when I still rode on the school bus, there was a kindergartener who shared the stop with me. His mom and my mom became relatively friendly. Once, after there was some issue with the bus driver, his mother said, "That bus driver thinks he's so great - he's just a f**king bus driver!" Right in front of her child. I kid you not.
When I first heard it, I completely did not process for a few seconds, I was so shocked that she would say such an extremely strong word in front of her five-year-old child. (She also had a three-year-old in the house.) Once I did process what she said, I was shocked and appalled. Wasn't she at all afraid that her child would repeat what she said? Did she really want her child to walk around cursing out the world with a word like the f bomb?
While there are many people who feel there are no problems with cursing, most feel that you have to curb your tongue around children, since bad words are simply inappropriate for little ones. I feel that cursing is inappropriate for all people, but especially when there's a child around. (I talk about this on the Bleep! site on the Little Children and Cursing page.)