I would be very careful about offering any kind of monetary anything. That could be misconstrued and if the parents did take you to court, it is an admission of guilt on your part. I know that sounds incredibly paranoid, but crazier things have happened!
I would arrange a face-to-face "I'm sorry-I forgive you" moment, but that's it. I'd also be sure that my child never EVER had the opportunity to do that again, plus understands the very serious consequences (it actually can be charged as an assault) I'd also want to know where the adult supervision was at the time this happened. That would be my biggest concern.
BTW, I have 4 DDs, never cut anyone's hair, never had theirs cut, so I don't think it is necessarily a "rite of passage" and I would NOT find anything "cute" about it.