"kids" should never have administrative privileges on the system (up to the point they can burn a CD - then they can have admin privileges because with enough googling they can do it themselves). And you might want to install a sandbox type program - http://alternativeto.net/software/deep-freeze/?license=free
Windows is a consumer operating system. You and I may know the "right" way to use it, but mother-in-laws don't like passwords, kids like Minecraft, and kids = chaos.