We live about an hour away so we usually only visit the museum annually. My children are now 7 and 10 and we just came back from our spring break visit. My kids played so hard in the 4 hours we were there they both fell into bed exhausted that night. Their favorite areas are the ant town, the shipping/receiving area, the water area, and the mock-town where they could pretend to run a grocery store, a restaurant, and a number of other occupations. They also love the little art room, which has various activities.
At $10 per person young or old, it can get to be a bit expensive. They will validate your parking ticket if you park in their garage, which saved about $4 off of the parking fee. If you live close by it might be worth it to look into a membership to save money over the course of a year. One nice thing is they have a coat room to hang coats so you don't have to spend money on a locker rental (come to think of it, I can't remember seeing lockers- if that's a concern best to call and ask).
It can get crowded so if that's a concern I'd recommend calling to ask for best days and times to avoid crowds.
One minor quibble, I wish the gift shop had more kid-friendly prices so kids could spend some of their own money (mine love to shop on their own). Everything in there is way over priced.