Online privacy & safety for kids

Part of my job is ensuring the online safety and protection of privacy for users aged 11-16 (soon to be 9-19). Given the wide age spread I've had to be really careful about how I set up the chatrooms etc to ensure that we comply both legally with country specific requirements, and general good practice on safety.

We've received some good advice in the UK recently (from sites like ww.thinkuknow.org) but the info we have is all based on younger students (5-10 year olds) and it's pretty patronising for 12 year olds. My particular audience is quite sheltered in lots of ways and therefore a little less streetwise than I'd expected so I'm having problems figuring out the best way to address the problem. Has anyone else been through this who can share wisdom (or even just a place to start looking?)

NB we have built in some protection to start with, they have to prove age (by member application) before they get access, access is rescinded if they break the rules and all conversations are monitored (although on an intermittent basis). The biggest problem we have had has been them starting their own groups on other sites and then meeting up (and doing those things that teenager's parents don't think they would do).

Thanks!

Rachel