I don't know how involved you would want to get, but another suggestion is to go to the school they attend, sounds like you know what school it is, talk to the prinipal about how shameful his/her students are acting to a 5 year old. (Is that what their teaching them there?) And that you want him/her to talk to their parents ect... shouldn't be hard to find out who they are if they take the bus often. I know that's a very bold move (that's what the mother bear in me would do)

Good luck, more hugs for you smile