As others have suggested, simply taking the device after bed time is probably your most bullet proof option. In lieu of that, setting up rules on your router o

As others have suggested, simply taking the device after bed time is probably your most bullet proof option. In lieu of that, setting up rules on your router or firewall to disallow all network access to their IP addresses after bed time. Better yet, to all addresses not on a white list. Might occasionally be a pain for overnight updates though.