It totally depends. It was 38 here in KY last night and my DF in Ocala, FL said it was 38 there, too. Now it didn't get warmer than the mid-50's here, but I bet it got in the 60's there. We lived for 3 years in FL and the weather was all over the place. I did get a mosquito bite on Christmas, so that should tell you how seldom it actually freezes. Ditto all the people who said bring layers. Plus, WDW gets cold when you go from dark attractions to back outside so bring something you can get off and on easily for you and the kiddos (cardigans, etc.) and wear it around your waist.
BTY, when is colder than 65, and you see people wearing heavy coats and gloves, those are the Florida residents. When you see people on the same day wearing shorts and t-shirts, those are the Europeans and the Northerners....We never used our pool when it got below 70 degrees outside, but all the people who visited us were swimming fools because the water was so warm to them.