FJ, I mean this in the kindest possible way, but I think you're worrying too much about this hun. When Lindsay was in kindergarten they went to see a play in a town that was 1.5hrs away and they travelled by bus too, they also had another trip to an environmental teaching centre which was further still. Not all seats had seatbelts either. You would be surprised at how well behaved they will be - the teachers do a pretty good job of making sure that no one is up running about the bus and when I was a kid and went on trips we were always given games to play like car cricket and singing etc. If you really do feel that strongly about it, then by all means ask if you can drive him there, or alternatively if you can go on the bus with them.

ETA - if travelling back in peak hour at least you know they will only be going at a snails pace