Hi Diane Elizabeth! Thank you for reaching out to the Disney Parks Moms Panel. Your trip is right around the corner - you and your granddaughter must be getting so very excited!
Currently the weather is very cold for Florida (40F/4C) but good news, it's expected to turn around and be nice again by the time you get here. The estimates for your arrival show 65F/18C during the day and 50F/10C during the evening. And if its a very sunny day it will feel that much warmer out.
If I were in your position, I would decide on the number of outfits I wanted to pack (or that my suitcase allowed) and then I would keep the articles of clothing to the following per person:
~ Half of the tops long sleeve, with the other half short sleeve that pair well with a jacket, sweater, or sweatshirt.
~ Two additional light to medium weight jackets (bonus points if one doubles as a rain jacket) for early morning and evening/nighttime activities. You'll want items that you can layer on should you get cold but aren't too bulky that you have a hard time carrying them around with you should you become too warm.
~ I would keep the majority of the bottoms to jeans or long pants.
Don't forget about a pair or two of comfortable shoes, AND also pack your swimwear as the majority of pools at all Walt Disney World Resort Hotels are heated to an amazingly comfortable 82F/27.7C year round. And lastly, every resort hotel has an area where you can do laundry, so you can reduce the number of items packed to save room for souvenirs.
Rest assured that should you forget anything every resort hotel has at least one very well stocked gift shop, and
World of Disney at Disney Springs is the Western Hemisphere's largest Disney Store.
I do hope that you and your granddaughter have the most magical trip, Diane Elizabeth!
~Kristen