How to setup functional network based internet parental control?

I'm firmly in the camp " Teach kids to swim rather than keep them away from the water". Nevertheless due to strong suggestions from SWMBO I'm looking into setting up parental controls. Being the geek dad my requirements tend to be more complex. First of all we have a zoo of internet capable devices: PCs (Windows, Linux), Mac, iPhone, PSP, WII, DS and even a OLPC. The gentlemen switch between all these devices. On the PCs and Macs they do have their own accounts. So a parental control needs to be implemented on a router level (I would be OK with dd-wrt or OpenWRT.The general idea is to have a time and duration based access. So based on school day / weekend / holiday there would be a time from to where the internet is open. There would be also a time limit for total access (e.g. the Internet would be open for 12h/day but total time might be 2h only). On top of that there would be a list of constraints and extensions:

• Obviously there is a permanent black list. I don't want them to surf to adult content
• There is a permanent white list. Places like The Khan Academy, OpenCourseWare Consortium, the MIT, their own School, The yellow bubble or comparable sites would be available any time (even outside the core internet time) and would not count against the time limit.
• There is a "gray list" that list sites (like battle.net) that are only accessible during "off hour" periods. Off hour would be a time frame inside the general opening hours (or its own time slot if that is easier to implement). Gray listed items could have their own time limits
• For the devices with user accounts I would expect no authentication prompt but an automatic propagation of identity (am I dreaming here?) from Win, Mac, Linux. For the devices without user identity (iPhone, WII, DS, PSP) a authentication prompt would be required (more dreaming?) - or alternatively: have their own Ethernet-ID bases access control
• Special challenge: a lot of site (like the Khan Academy) store content on YouTube. But YouTube also hosts content like the annoying Orange. How to allow the former and block the later?
• Bonus challenge: have a request mechanism where they can click and request an URL to be added to the permanent white list

What would be a workable approach to implement this?
P.S.: Now If I could control the TV as part of the setup (I rather have them surfing or playing WoW that couch potatoing.