Hey Jenni! Three is a perfect age for a Disney fun vacation! You will find that your ten month old will also enjoy the stimulation that will surround you during your stay.
There are attractions in each park that are geared to all ages or just the younger set. If you click
HERE you will find the ATTRACTION main page. On the left side check RECOMMENDED AGES and then click on PRE-SCHOOL. This will filter a list of those things that are geared for that age group through-out the property. That doesn't mean your daughter will love all of these or that there aren't other things for her to do but it is a good place to start when planning.
There are child care centers in each park which you will want to locate on the map as soon as you arrive. They are wonderful spots to rest with the baby and toddler and they will have all those supplies for sale including foods and formulas that you might accidentally leave back at the room. There are nursing rooms as well as changing stations and relaxation and play areas.
I strongly suggest you consider sending some of the important supplies that are bulky for packing on ahead of your stay. Or you might consider using one of the great grocery delivery service that is available for all resorts. I have used gardengrocer.com before and have found their service excellent. You register on line and then have pages and pages of food and baby items available to purchase to be delivered directly to you. This includes formulas and of course diapers. If you are in need of renting a stroller or other baby equipment during your stay then I would suggest you check out the orlandostrollersrentals.com. They offer a wide variety and deliver and pickup from the resorts.
Enjoy and be sure and get some character dining reservations for your vacation. Pack plenty of film for all those great photos you will get with your two children!