We drove about an hour or so south and went on an airboat tour through mangroves. Also there are a couple of good miniature golf places for once sun goes down on the way to Fort Myers Beach (one of them is sort of R rated with the animals and yes your boys will notice).
Sansibel beach is good for shells.
Last year when we were there the water was shut down due to red algae.
Good food at Doc Ford's and Pierside Bar and grill.