Your friend in this scenario is committing fraud and/or theft. They're obviously not going to be your friend anymore, unless it was a mistake they immediately correct when notified and pay you back the money - or you forgive it. The bank can go after them and sue for the money/file charges otherwise.
Can/should the bank go after your child? Or does it make more sense to say that yes, you are liable for the charges your child makes? Or do you suggest that we simply accept that kids charging money to their parent's account without permission is something society should pay for?