Lambourne
Ahn'Qiraj Raider
We are trying to plan a trip to Florida with kids late February / early March. We know absolutely nothing about Florida.
The best example I can give what we are looking for is something like Kauai (less city, more nature, clear warm ocean). I understand that Florida != Kauai but didn't know if anything like that existed or what our best options would be. I also am not sure what the water is like in Feb/March.
That early in the season I'd probably go to the Keys if you want to sit on a beach/swim in the sea as there can be a fairly substantial temperature difference between central and southern FL that time of year, 10-20F higher in the south isn't uncommon. Don't have a specific place to recommend since it's been years and years since I lived there but there are tons of resorts along the Keys, don't focus on Key West only (it's also one of the most developed Keys, most of the other ones have far more undeveloped nature remaining). South Beach in Miami I thought was overrated and doesn't really fit your nature criteria anyway.