My kids like this game alot... The Way things work.

http://www.amazon.com/INTERNATIONAL-PLAYTHINGS-LLC-THINGS-WORK/dp/B001EY5PRE

My 6 year old plays too (when he was 5 even). He still finds it fun even though the questions are kind of hard for him. The questions are all multiple choice, so he takes his best guess but it's a great, fun, educational game about... well... the way things work!