I dont care how ambivalent your teens may be about a family vacation, you put them in the car and drive across this bridge and they WILL sit up and be amazed. This is a jaw-dropping ride, sort of like flying, as you cross this bridge high over the every-changing variations of turquoise waters below. And bonus - every single time you make the trip, your view and experience will be completely different. Guaranteed.
If you have time to stop and get out of the car, even better. There are many, many mysteries just below that water. Dolphins, turtles, manatees, stingrays and any number of fish to see.
If you wonder what that little island is that you see below the bridge - that's Pigeon Key - and you can go to the Pigeon Key Visitor Center (north of the bridge) to buy tickets on a ferry to check it out for only $12 a person. It's a beautiful boatride to a historic location where the kids can run free - everyone wins! If you want to stay around this area, Bahia Honda State Park is just south of the bridge where you can rent cabins or camp out and enjoy a couple of days getting immersed in the culture and beauty of this amazing area.
Bike or walk the bridge if you have more time! It's really iimportant to realize there is so much more to the Keys than meets the eye. Take time to relax and take it all in.