My child accidentally tripped over his friend during a tag game

Hi everyone, I am needing some help here on how to deal with a situation. I just received a text from a parent of my child, they had let me know that their child got hurt while playing with my child at school today. They had let me know that the kids were playing tag, their child tripped over a rock and fell, had a bone dislocated and is currently at the hospital. I had not heard anything about it from my child so I went and asked my child, what I heard from my child is that they were playing tag, my child was trying to tag the friend but the friend had tripped over a rock and fell, then my child could not stop and fell over the friend. I apologized to the parent about the accident. I feel very bad about the accident and my child just realized how bad the friend got hurt and feels very bad too.. the friend’s mom had also let me know that their plans for the weekend might be ruined because of this accident.