School Bus

I like the idea of the school bus; someone else drives my kids the 6 miles to school, I get to add an extra 20 minutes each way to the school day (read: time without kids fighting). However, somewhere along the way the idea goes wrong.
We had problems at the beginning of the year with Tristan being picked on. Brian and I decided to wait and see and try and get him to handle the problem himself. We felt that he needed to learn to defend himself (verbally) against bullies and this was as good as time as any. Those problems have been solved.
The other problems have become noticeable more gradually. Jack has learned several inappropriate songs on the bus. Tristan has asked me about several creative swear words that he's read written on the seats of the bus. These buses are brand new. It irritates me that the kids destroy them so much. My neighbor girl, who's a wise 10 year old, told me that someone has written the "f word" in permanent marker all over the back of the bus. In addition to this, the kids fight, yell, swear and generally act terribly the whole way to and from school. I told Brian I think it's mob mentality. The kids do things they would never do on their own.
I talked it over with Brian (who is my litmus test for rationality) and we decided just to drive the kids to and from school everyday. They don't need the exposure to all of that to and from school. They'll get it soon enough... Jack doesn't need that in kindergarten. Call it over-protective I don't mind. We'll see if it improves their attitudes afterschool.