I am wondering by the way, if this problem should be tackled through Firefox. As we say in the Netherlands: "don't start mopping the floor when the tap is still running". Maybe the original poster *did* manage to remove the add-on, but something else is causing it to reinstall again?

I remember a case where someone had a particularly nasty piece of adware on their system that flooded every available pixel on the screen with toolbars. No matter what I tried, it would keep coming back. It turned out that a small bit of malware had buried itself good and deep into the system, and kept re-downloading the toolbar when it was removed. Took both AdAware and Spybot Search and Destroy to get rid of the little bugger.

I'm curious if the children just downloaded an add-on, or if something else tagged along for the ride.

Same thing happened to me when I inadvertently gave permission to the infamous Microsoft .NET Framework to install itself in my profile, it was really annoying to remove again. I fixed it by editing the about:config option that lists the installed plugins. But there was nothing Firefox COULD do to help me, because the Microsoft people designed .NET to hack Firefox to prevent uninstallation. If you allow little kids to run programs as admin, the same thing happens: it can install malware on your computer, AND hack Firefox. How are Mozilla supposed to stop you from running programs that edit their application?

The only solution is to not run untrusted programs as the admin. And obviously, don't let your kids do so either.

My advice: start them on a linux OS. Even a luddite can't accidentally let their kids do this kind of stuff on linux. And Ubuntu is very user-friendly to the luddite mind.

Or as has been mentioned, give them a limited-access account. But you should still try Ubuntu, because it's really good and Micro$oft tends to do these things to you.