Quote History Quoted:
How old are they?
Maybe teach them how to use a LiveCD so they can't get possibly harmed by it. A LiveCD has a whole operating system on a CD rom or DVD and it doesn't have access to the hard drive. Pop it in, boot, do whatever online, remove CD and reboot and nothing can touch the Windows behind it.
Tell them "For gaming sites that might try to infect your PC."
View Quote
I agree, I VM would only work if you kept it just as protected as the actual PC. Best bet would be a LiveCD/DVD/USB with a free Linux distro (I'm sure they can figure it out).
If your ok with what they're doing on the interwebs, then they could store all important files on a NAS or ext.HDD and run Linux, then you could reload in a few minutes if need be.
Good AV and security practices are always the best bet, training and trust will out do any physical devices you put into place.