My boys, ages 5, 4, and 2 LOVE the Orlando Science Center! It is something we do every time we visit.
We are members here in Ottawa of the Museum of Science and Technology. Our membership here allows us entry to the OSC for free. Check to see if your local museum has a reciprocal agreement! The cost of the membership here for the year is the same price as entry for one day at the OSC. WELL WORTH it.