With that many people, I definitely suggest renting a van. There are several car rental companies within 3 miles of the pier. They'll pick you up and drop you off for free. It'll definitely be ALOT cheaper than purchasing any excursions, that's for sure!
The Kennedy Space Center is only about 20 miles away and is wonderful for kids of all ages.
Disney world is only 65 miles away, but you really don't have enough time for that considering you'll spend about two hours driving there and back. Same is true for Sea World.
Unfortunately, there's just alot to do in the immediate area, so you basically are limited to KSC or the beach - and there are some nice beaches in the area.
__________________ 46 Cruises & Counting! Favorites: Paul Gauguin to Tahiti: Uniworld River Cruises in Europe; any of the Celebrity Solstice-class ships; Holland America for 12-nights in the Baltics & Russia; RCCL for 14-night Greek Isles, Turkey, & Croatia; Holland America for 14-day Alaska cruisetour; 10-night Canada/New England cruise; 21 days in Hawaii including a 7-night NCL cruise; Oceania for 25 days in Asia; & 3 months touring Europe by train. And many days spent in all-inclusive resorts!