They also have rotating exhibits. The first time we went, January of 2011, the rotating exhibit was a Vet's Office. This last time, February of 2012, it was a Physic's lab with wind tunnels and plane launchers.
A large part of the first floor is dedicated to the really young children. It is designed for the infants and toddlers in mind. There are cushioned areas to sit, places to let babies crawl, and play structures that are easy for young toddlers to climb on.
Here are some pictures from our first visit right before my daughter turned 2.