In ideas on equipment and software?
Three words.....
Faronics Deep Freeze
Then, no matter what weird and programs they download from questionable sources, all you need to do is reboot and you're back to a known-good config (once you've done the prep work of setting up that config to your liking and frozen it, of course) It's the sort of thing they use in internet cafs, libraries etc..... and not as expensive as you think for a basic implementation.
Should work wonders combined with the usual lockdown precautions of user-mode accounts, BIOS passwords and disabling USB/CD boot etc. etc..
As for what you use to stop them viewing porn, well that's up to you. There are a multitude of options out there. Saab's one of using something like OpenDNS sounds better than using some proxy software on your PC ..... what happens if your PC breaks ? You want to minimise easily avoidable SPOF's and excessive management time. Plus if you go the PC control route, and they find that out, it's going to be their primary attack target !
As for equipment ? Panasonic Toughbooks are probably just about teenager proof !