My take is that current systems are far too hard to deploy and configure. Otherwise this question would have stopped repeating.
How about some parental control software. There's what is in many versions of windows as well as K9.
I have a modem/router but I'm thinking it'd be useful to plug another router in to a spare rj45 and create a seperate network for my kids to use. It'd be good to be able to allow access in a timed fashion via done sort of login/voucher (similar to hotel wifi) - any help appreciated in the best way to achieve this, both hardware and software