Obscenity Found Its Way

to our school bus. When I was younger, I only rode the bus for 2 years, in 7th and 8th grade. Otherwise I was a "walker" and trudged 10 miles to school each way, uphill, in the snow. Well... not really 10 miles, more like 2. And not uphill both ways, just one. But the in the snow part is totally true, at least for about 4-5 months out of the school year. Anyway, my 2 years on the bus are fairly unmemorable, except for the really cute neighbor kid that used to sing a song with my name in the title. No fights, no foul language, no rude or crude gestures. We waited at the stop, rode the bus, period.
Nowdays, things are a little different. Namely, in our small county, all the kids ride the same bus at the same time. In some ways this is a good thing- my older kids can look out for the younger ones. In some ways this is bad- my younger kids are now being subjected to the rantings of some very crude and undisciplined teenage boys.
My older child wrote a blog entry that detailed some of the language used on the back of the bus. Amazing! If I ever heard one of my kids talk like that I would wash their mouth out with soap. Either these kids parents don't realize what they are saying when they get on the bus, or they don't care. Rumor on the street is, the second scenario is more likely. Our bus route is said to be the "worst in the county". In fact, the Sheriff has been called upon before to follow the bus along it entire route from the school. A glimpse into the back of the bus reveals why. Now, I don't care if these kids want to use that language while they are at home, or hanging out with their buddies- I'm not their mama and it isn't my place to stop them. But- when they use that language in front of my kids, especially my 5 and 7 year olds- that is totally unacceptable. The problem is, what to do. If I throw a big fit, chances are some of the foulness will get turned on my older child who is in 8th grade. But if I don't, am I really protecting my kids? Is it enough to tell them that those words are not appropriate and shouldn't be repeated? I'm not saying my own language is pure, sure, sometimes I say things I probably shouldn't. But then again, I'm an adult. To every thing there is a season (turn, turn, turn)- and if I want to swear when some jerk pulls in front of me and nearly causes a wreck I can do that. But I'm not riding a bus with 30 kids under the age of 9 either.
So, what do you think? Am I being the overprotective helicopter parent? Or am I still the free range parent trying to set some limits on what my children are exposed to at appropriate ages? And how do I address my concerns without having this troupe of badly behaved boys turn on my kids?