I unfortunately have been involved in several rear end accidents. It is up to the person behind you to stop no matter why you are stopped. It's called assured clear distance and/or failure to stop. His insurance should have to pay no matter what. If the police cited the boy, I don't think there is any way they can get out of paying.

In one accident I was in, a person in front of me stopped to turn left. I stopped but the person behind me didn't. She hit me and pushed me into the person in front of me. The person who hit me had to pay for both my car and the car in front of me and they are the ones that got cited. Thankfully the person I hit told the officer I was stopped and so did a couple of witnesses.

I am so very glad that both you and the baby are okay!