In Harry Potter books, what should the three Malfoys' punishment be for helping Voldermort?

They seemed to get off scot free.....even though all three actively conspired to do harm against Potter and others...only when they got on Voldermort's bad side and started worrying about their own safety, did they appear to express reservations...not sure that entitles them to a free walk, from either American-style criminal justice, or even Azkahban criminal justice system.