Most of the time this is a exercise in futility. What I would do is install a browser history app and check and see where your scion has been surfing. most any filter can be bypassed but the threat of losing the Touch if you find out he has been where he should not have been might just work better for you. In the meantime go into the parental controls and set things up there to suit. To quote President Regan "Trust but verify"
We have been using a service called Mobicip and have been quite happy with it. It does exactly what you describe - offer a filtered web on the iTouch. Note that it doesn't filter Safari itself but since Safari can be locked out using the restrictions feature, Mobicip will be the default browser available. Check it out at www.mobicip.com. We signed up for the premium level for better control and monitoring ability.