Ah great route
for a family cruise
. You can day sail as far south as 10,000 Islands with lots of great stops in between. Bit longer run then to Dry Tortugas
or Key West (90nm from Ft Myers Beach to Dry Tortugas
as I recall).
From Lonboat Pass its a long day sail (depending upon your boat and conditions of course) down to Boca Grande and on into Pine Island Sound...great mini cruising ground here all the way down to Sanibel Island. Cabbage Key and Captiva Island are cool stops the kids should enjoy.
The DT's are great but could be a bit arduous for a family outing on a small boat. Its not far but the seas here can get short and nasty due to relatively shallow water
and currents in this area. Lots of trawler
traffic between Ft Myers and the DTs at night. No water
available there either.
Not sure how far you plan to go in the Keys but w your draft
you should be able to get into the Pennekamp Park mooring
field. Great spot and the kids should love it.
Have not cruised this area in many years since all the anchoring
issues started in FL but others can give you more current
info on that.