The Children's Museum is a great place for kids of all ages, but seems best suited for those between ages 3 and 9. They do have one free day per month, but it is very crowded on those days. The admission fee is well worth having a bit more space in which to explore and play.
High commendations to the staff. They are alert, and attuned to the children that are there. Recently, I watched a child who couldn't find her mom, and the child started to cry. I noticed that a conscientous staff member followed her until she was reunited with her mom.
The wide range of exhibits keep children entertained for hours! Our favorite is Earth World, where one can crawl through ant hills, and hide in a wolf's den, make thunderstorms, and investigate a swamp. I would recommend wearing jeans or pants, however, to avoid rugburned knees in the ant hill...