Son Accidentally Hurt Another Child

Location: Maine

My wife took my 5 year old son to the beach yesterday where he was playing with another child he met there. They were playing with rocks and apparently my son went to put a rock up on an elevated platform and it slipped out of his hand and fell backwards. At the same time, the other child was bending over to pick up a rock and was unfortunately hit in the head. She had a pretty good size bump and was taken to the ER where she was diagnosed with a concussion. My wife was in the immediate area but did not actually witness the event. The other child's mom was not in the immediate area and did not witness the event. There were others that witnessed the event and confirmed it was an accident. The other child also confirmed it was an accident and she was very upset thinking that my son was going to get in trouble.

Through a mutual acquaintance, we found out that the mother was trying to get our information. She actually said it was the hospital that needed our information, which I believe is most likely not true. I am assuming they are going to want to be compensated. I've already contacted my Home Owners Insurance to give them a heads up.

I do not believe, based on what I've researched, that I would be legally liable for this, but was looking to confirm if there is risk of a lawsuit.

I was also considering having my son give the other child flowers or a card to express our hope for a speedy recovery, but I've received mixed responses to that. We truly feel awful that this happened.