We went to the American Museum of Natural History which is by far my favorite museum. Its huge and takes most of the day to see. We started to crash and burn before we saw everything.
After the museum we went to the flagship FAO Schwarz store for my youngest sister. They had the biggest stuffed animals you could imagine and the giant floor piano that was in "Big." The picture is of a huge toy soldier made of jelly beans.
For my middle sister we went to the Apple store, luckily right next to FAO. Its the really iconic store that is beneath a glass box, definitely a cool store to visit but we were all exhausted by that time.