This museum is truly special. There is SO much to see and do, and exhibits are always changing. Exhibits are exciting, interactive, and (don't tell the kids) educational. My husband and I went (yes, 2 adults) on a random day off from work. We were there a couple hours and basically just walked through the museum. We didn't stop to browse a whole lot, but if you did, you could be there a long time!
If you are a local, I recommend the museum membership, esp. if you have kids. The museum is so big, I would think young kids would get tired out after hardly seeing anything. Memberships allow you to come and go without feeling like you are wasting an entrance fee. For visitors, plan to spend all day here and take breaks as needed. There's a cafeteria but also a place you can lock up your own lunch, etc. Take your time and be selective about what you and/or your kids want to see (dinosaurs? Science stuff? rock climing wall? planetarium) and take the time in those exhibits to make the most of it.
Above all, relax and have fun! Watch the wonder light up on the children's faces (regardless of the age)!









