How much do we love this museum? At least once a year we make the 3.5 hour drive and stay in a hotel just to visit it!
My boys (7 & 8) love it and have loved it since they were much younger. Now that they're older, though, it's MUCH more fun. They actually can make cool things now -- use circuits, sew, paint, silkscreen, weave -- you get the idea. And they get the broader concepts behind the exhibits (gravity, engineering, etc.).
The staff here are excellent and always willing to help show us how something works or to get the kids involved in whatever they're doing.
Bottom line: this place is great for kids of all ages, but I'm really seeing the fun now that the kids are a little older!