If you are down that many days I would say that you should visit all the main keys. It's definitely a great vacation time for the family (including all ages you mentioned) so long as they like water and marine life like oscarreef mentioned).
I go down to Key Largo so that's the one I know best so I'll start there:
Key Largo:
- Best snorkeling/diving in keys (Rainbow Reef probably the best outfitter imo). John Pennekamp state park is one of the largest protected reef areas in the world and has really improved drastically over the last few years with all of the conservation efforts.
- Restaurants: The Fish House, Hobos Cafe, Sundowners on the Bay
- Best Hotel: Marriott Key Largo (has a Jimmy Johnson's Big Chill which is pretty good also)
- Swim with Dolphins: I highly recommend this. The girls (and you) will love it. It's one of the best experiences anyone can have. If you do it, this is the place. Don't do it at Theater of the Sea (it's a major tourist trap). Theatre of the Sea is fun for the shows, but not a good Swim with Dolphins place. And well, it's an aquarium which I'm kind of down on now with all the stuff out there about how crappy they are. Go to Dolphins Plus in Key Largo. They are a research centered Swim with Dolphins facility. Dolphins get let out into the wild everyday.
Islamorada:
- Probably the best fishing in the keys. So if you're going to charter a boat do it out of here. While I am not sure the girls would enjoy deep sea fishing (easy to get sea sick), there is phenomenal back country/flats fishing. That said, if you can do both, do it. Those river fish you catch in WI; we use those as bait!
- Restaurants: Green Turtle Inn (Don't miss it!!), Key's Fisheries (especially if Stone Crabs are still in season)
- Hotels: No clue.
Bahia Honda State Park
- someone mentioned this and it is for sure the best (and really only) beach in the keys. You can camp here, but there aren't really any hotels per se. This is a day-trip thing and I would stop here on the way down to key west. It's also one of the most picturesque places in all the keys.
Key West
- Definitely the most touristy of all the keys. But absolutely worth going.
- Very walkable, great food, great key lime pie
- If you can pull off a day trip to the Dry Tortugas, do it.
- Also a great place to rent a boat and try some watersports if you never have.
- Otherwise, just walking around Key West is a great experience. And you'll be able to snap the obligatory photo of the family at the Southernmost point in the USA (90 miles from Cuba). Also, great museums. The Butterfly Garden is impressive and if you like Hemmingway and history, there's the Hemmingway house.
-Restaurants: If you want to give Cuban food a shot, do it at El Siboney.
Off the beaten path, but another can't miss spot is Hogfish Grill. There's dozens of other amazing places. Hard to go wrong in Key West.
Hotels: Pier House and Southernmost Hotels. Stayed at both within the last year. Can't go wrong at either.
As for scheduling and days needed at each key, they are all very small so it more so depends on what kinds of activities you want to do in each key.
Good Luck and hope this helps!!
