We went at 12:30 on a weekday, and crowds were still heavy in some exhibits, but they began to thin out by about 2 PM. I would not attempt this museum on a weekend or holiday. I think it is most appropriate for kids aged 5 to 12. There are a wide variety of exhibits with many hands-on opportunities, but not much more science than you would have learned by 9th grade. They advise starting at the top (a non-stop escalator takes you to the 4th floor) and then working your way down, but I think going in the opposite direction would have meant smaller crowds. Exhibits halls include dinosaurs, birds, fracking (the most boring for the kids), inventions (lots of hands on stuff here), gems, genetics, adaptations, and the sports hall (my son's favorite because he got to do a timed race against his sibling and do a sports move of his choice and then watch the video playback of his accomplishment in slow motion side by side a professional athlete).
If we went again, we would not bother to purchase the horribly overpriced World's Largest Dinosaurs special exhibit. This exhibit, for an extra $6 PER adult and $5 PER child (if bought separately), included only a few models (not even real skeletons, except for one leg), a fossil dig pit (the kids did enjoy that), and a small gift shop (in case the main gift shop wasn't temptation enough for your kids). We did not try the Design and Create special exhibit, so I can't comment on that.
The kids enjoyed themselves, and we will definitely be back to focus on the area where we didn't get to spend enough time. We didn't go into the children's museum (in the basement), but it looked to be geared toward the under 8 set. An overpriced café is available with a decent but pricey selection. Eat before you arrive. Bring a change of shorts for the kids because they will likely want to splash in the water outside in the mini-river by the leap frog structures. A sign there implores children not to jump or climb on the frogs. Are they serious?
We spent $84 for the 21-minute 3D dinosaur movie, exhibits, and World's Largest Dinosaurs combo for 2 adults and 2 kids, plus $8 for parking – a bit pricey overall for a museum experience, but we spent a good 3.5 hours there, and would have spent 5 if I had just been with my daughter (9-11 is the most ideal age for this museum, I'd say.)