Today we took our first adventure to Discovery Gateway. You can find all their information on their
website. Two of my nieces attend the same preschool, and they were having a field trip, so we were able to tag along. I think it is pretty expensive to go without a school group or discount of some kind, but we were able to go for the group price, so it was great! Because we were with a school group, we couldn't do certain things and they scheduled our time in each place, but we were able to play a lot.
My overview of the place is that the bottom floor is better for younger kids (pre-K) and the upper floor is geared for older kids (elementary), though kids of all ages can find fun things to do on both floors.
Fun exhibits there are: a store, house, farm-ish, waterway, balls with tubes, construction, news studio, blocks, theatre.
I think this was a fun activity, but all the adults were done about 1.5 hours into it. I think the younger kids were done shortly after that, and the older kids could have stayed all day. It was fun to go and hang out with my sisters and their kids. Here are some pictures that show some of the different things to do there.

Recommendations? I would probably go there again, but only if it was discounted and I had some friends and kids that wanted to go. Plan for two hours or less. There is no food or drink allowed inside, but they have some tables out by the helicopter that you can use for a lunch/snack break. You can get a 3 hour parking pass to park at the Gateway for $1 (inside the museum).