Hello,
As my 9-year old daughter uses its iPod Touch to access the web, I was searching about the same topic, and came across a number of ideas...
1) Wifi curfew
With the Centro router, you can configure when the wifi should be activated and when it should stop.
Ideally, combine it with 2 wifi accesses, 1 for the kids, another for the adults (not tried yet).
2) Use a filtered DNS server
For example, OpenDNS has family-friendly DNS servers that filter out explicit web sites. Might not be compatible with VDSL though.
Regards