That is a tough one for sure ... sounds like they are making progress in your program so there is HOPE but if it were me as a minimum I would be putting in place a 'behaviour and guidance action plan' with the parents - an amendment to the contract so to speak to help both child get some anger management skills and strategies in place and a TIME LINE for improvement for the aggression to STOP otherwise their contract will need to be terminated because the other children in your care should not be the 'punching bag' for these kids