moms with kindergarteners please help!

Stacey
So my son just started kindergarten. It's day 3 and he comes home with a bruised ear! He told me an older girl on the bus took his backpack and pushed him and his head hit the window. I'm so mad! Mainly because throughout all of orientation the principal made it clear that all the kindergarteners sat in the very front of the bus away from the older kids. Secondly, this little girl just HAPPENS to get off at our apartment complex bus stop and her mom is someone who is trying to befriend me. So I feel stuck in such a hard situation. If I didn't know the mom I could easily talk to the bus driver. But now I feel like I need to just talk to the mother myself. I feel so horrible for my son that he ALREADY is having to go through this. It breaks me heart, I can't believe it! They reassured us on how safe the bus is and how they've never had any issues with the older kids and on day 3 I'm realizing that is obviously not true. What would you do?