Delay the meeting.
1. Did you take your son to the doctor? (To check if damage was done to the eye)
2. Did your son behavior change after the incident? (Is he afraid of other people? Does he need to see a doctor for this?)
3. After the results of the above. I would then schedule a meeting with the parents. (Maybe skip step 2.) Then give the parents an invoice the cost of the doctor visit. (Optional)
I don't know all the facts just from what you told us. Maybe I'm over reacting, but from the pictures it doesn't look good.
Another question to ask: Is the scratch on your son's face going to leave a permenant scar? I would see a specialized doctor for that.