The "F" Word!

I've previously mentioned that this our kids' first time ever riding the bus to school since I no longer work at their school. I've posted a few stories about my worries about them being on the bus. I have to remember that all kids are not raised the same and people are products of their environment.
I have tried to shield them from as much as possible. Sure at their ages I knew a whole lot more than they did but those were different times (1970s) and my environment was much different. For example, I was all over the neighborhood playing from sun up 'till the street lights flickered on, and my mom did not have to be within eyesight. I learned how to skate and ride a bike simply by getting out there with myriad other kids in our apartment complex. We fell, dusted it off and kept trying until we got it. Don't remember wearing helmets either. Now, our kids better not leave our yard and we are either on the porch, or somewhere nearby.
Well in our house some words have been considered as bad but of course in other homes this may not be the case. Other kids may know the "real" bad words.
So as usual they spring something on me while I am driving. "Mama. This boy said the "F" word, this morning on the bus," our son said from the middle seat. So, being the sometimes paranoid mom that I am, I swerve a bit. Panicking, I first turned the radio up louder instead of down.
"A boy said what?" I yelled. Once the kids took their hands off their ears, his sister chimed in.
"Well actually he said two, bad "F" words!"
I am looking at the road in front of me and looking in the mirror at them- back-and-forth.
"Did the bus driver hear them? What did she do?" I asked them.
"I don't know if she heard him but the other teenagers heard him," our son said.
They are in elementary school so I didn't know what he was talking about when he said teenagers. "What grade were these teenagers in?" I asked. "Oh they were in the fourth or fifth grade," our daughter answered. "They are not teenagers," I told them. "They just probably look big." Our daughter thinks that kids are teens if they are taller than she is.
Finally we get to the meat of the story. I was afraid to ask but I did. "What did the boy say?"
"Mama. I don't want to say it. It's bad," our son said. "You promise I won't get in trouble for saying it?" he asked, closing his eyes. Then our loose-lipped daughter jumped in again. "I'll tell you what he said!" I was on edge. How could little elementary kids on the bus say the "F" word. Where had they learned this? Finally our son rushed in to tell me to beat his sister.
The "F" words were fool and fart. Well... they are bad words in our house.