A day at Cocoa Beach or Daytona Beach
The Orlando Eye, Sea Life Aquarium, Madame Tussauds Wax Musuem (combo tix that include admission to all 3 attractions are just $39 pp)
Fun Spot (two locations, Orlando & Kissimmee....your all-day wristband gets you into both parks all day long) - I believe passes are being offered right now on Groupon at a pretty decent savings
Wild Florida (air boat tour and exotic animal park)
Rent jet skiis through Makaio Watersports and spend a couple of hours on one of the beautiful lakes (due to ages of your kids, mom and dad would drive and the boys would ride as passengers)
Gatorland
Showcase of Citrus (ride in a Monster Truck through a real working orange grove, and enjoy a fresh all-natural orange slushie from the country store afterward) - discounted passes are often offered on Groupon or Livingsocial
Discovery Cove (full priced admission also gets you complimentary 14-day access to both SeaWorld and Aquatica)
Mini golf....we love Congo River, Hollywood Drive-In Golf at Universal (they have a fabulous Meal & Mini Golf offer: Margaritaville for dinner then golfing afterward), and Pirates Cove.
All of the above we have done with our teenaged son, and they have been big hits.
Other ideas that are still on our to-do list....
One of the many escape rooms in the area
Zombie Outbreak on I-Drive