I come from up north where the ocean temps never got over 60 degrees in the summer!
The water's a bit chilly (for us Floridians) but there's still all kinds of people in the water in March. Once you get in you get used to it anyway.
Florida weather is so unpredictable...some Easter breaks are warm...sometimes we have cold spells.
Two weeks ago for the Superbowl/24 hour race it was downright COLD....40's! Last week for the Daytona 500 it was around 80 every day!
It's always a good idea to get a place with a heated pool...but not necessary really. Teenagers will always find something to do if it's cool....and I can guarantee you NO SNOW!