We had an interesting day trip to a place called Homasassa Springs in Florida on the Gulf Coast when D1 was about the age of your kids. It is a state park. We rode on a boat into the park. They had gators, a hippo, flamingos, and you could go underwater and see manatees swimming above your head in the lagoon. As of July 6, I see a report online that the oil spill has not affected the area.
http://www.homosassasprings.org/Homosassa.cfm And my dad made arrangements for us to go on an airboat ride not too far from Cocoa Beach (on the Atlantic side) one year, I think it was on the St. John's River. That was very cool, and our kids loved it. There are several places if you search on the internet.
Also, north of the Kennedy Space Center, there is a very interesting drive if bird watching appeals to you. It is in the Merritt Island National Wildlife Refuge. We saw tons of stunning birds last spring.
