there are a number of restaurants on the bayside where you can tie up for lunch, that's always nice. with a 24 footer, the Penencamp park is a great option, you can go under US1 in to largo sound and go back and forth
there are some nice places to anchor out, just north of KL, you can go on the north sides of some of the empty keys, (butternut, etc...) and feel like you are far away from civilization.
islamorada isnt' that far form KL, at 24 kts, it's abut 45 minutes, you can anchor off Plantation Yach Harbor marina, there is a little beach there with a watersport shack (bay side).
btw, with kids, PYH is much better than HI.. there is a big swimming pool, skate park, Basket ball court, trails, etc... great place for kids. they are rebuildign part of the marina right now, but i think they are open.
it was interesting the first time i went down there with the hatt. a few years ago, i only had expresses before and never knew what was behind the mnagroves in the various channels... i was surprised to see a lot of water an not acres of taller mangrove...
i love the keys, it's so relaxing... time stops once you pass the jewfish creek bridge.
it's not a bad run from FTL... beats the traffic jams in the ICW and the unless you come back after a front and face northely winds in biscayne bay, it's a pretty smooth ride even with a smaller boat. i used to go down when i had my 25 footer...