Parenting 'Tweens (9-12) Support Group
This community is focused on the joys, challenges and concerns faced by parents of tweens (9 to 11 year olds). The major areas of child development include: physical development, perception and sensory development, communication and language development, cognitive development, emotional development and social development.

If you are worried about your friend and the circle of friends that are involved, then just be cautious about how you approach it, and be sensitive to everyones feelings that are involved. At the same time, your friend needs to know what kind of affect this is having on your child. After all, I would hope that she would not want her children to feel the way your son does, or be treated that way. You do need to say something about it though..otherise it is just going to continue and may potentially get worse.
Good Luck to you and hope all goes well!
If he is going to act like he's 4, then he is to be treated like he is 4. The parents would intervene right? He is plenty old enough to know you don't torment people on the bus...maybe subtly remind him the cameras RECORD everything on the school bus, and some have sound...that one's worked with my kids...(which, we do have cameras)
Anyway, talk to her about it, tell her it's been going on since school started, you tried to let your son handle it, but now it's gotten out of hand and is affecting his day more often than not, so if she would please talk to her son about it - that would be great...IF you sense her reaction is negative, or defensive, throw it out there that you know boys will be boys, but your son has a lot on his plate this year and doesn't want the added stress of the bus situation...leave it at that.