iPod, Itouch, iPhone, Iporn; any way of making parental control for these devices?

my teenagers both have the Itouch, the telephone-less version of the iPhone. Everything is password-protected and I can't even get to use it without their being around to open the device for me. Is there a way of inserting a parental control filter to avoid WiFi download and viewing of pornography and other objectionable material.

Basically these things are small computers that have all of the wi-fi abilities of laptops but without the Windows-embedded parental control of Windows Vista, for instance.

Is every kid going to have, effectively, an infinite pornography library in his back pocket?

Much as some adults might find that desirable, we're talking about minors here, and at the very least they should be having to work a little bit harder to get into trouble.