I'd say crowds will be close to normal.
The Orlando/Tampa schools have spring break March 13-17, and 20-24 respectively.
The South Florida schools have spring break April 10-14.
School calendar is here. http://www.fldoe.org/districtcalendar/
SWF is a more relaxed park to visit. Show up at 08:30am. Rope drops at 09:00am, and you walk back to Kracken and JTA. After that, it's all shows. Arrive each one 20-30 minutes early for the best seats. Go to lunch at 11:30am to beat the crowd. Even if you are not hungry, go, and by the time you sit down with your food, you will be.