Do The Math

Next time your kids would like to 'play' on your computer or iPhone, you could make sure they have one, or you could make sure they learn something new (while trashing you machine...).

http://www.thatquiz.org is a great website for teaching your kids Math.

Comment and warning :

http://www.thatquiz.org focuses on short, time based quizzes, on a variety of topics.
So, less explanation and more fun and getting points.
Make sure this would be good for your kids before you start with it.

Another option is http://www.gengarstudios.com.
BrainTuner is a great iPhone application (click the image for a direct link to the Apple store).
You can use it to stay sharp, or to prove to your kids that 3 hours sleep a night do not make you smarter...

A more generic brain/Math game is Brain Toot.

That should teach this kids a lesson...

E.T.