L.S.
If you're flying or have a full car, I highly recommend renting a stroller from Orland Stroller Rental. They will deliver and pick up the stroller to any hotel/resort in the Orlando area. They use comfortable jogging strollers - much better than the ones at the park at a good price. They have a double stroller that will fit an older child and your younger child as well and is good for napping. We're planning a trip next year with my 2 and 6 year old and I'll definately be renting a stroller from them again.
There is also a book about Disney with preschoolers that you can get at Amazon or maybe the library. It's got great advice about all sorts of things from attractions to how to plan your days. One thing we also did when we went with our daughter at age 3 was order snacks, sunscreen, and breakfast foods from a grocer that delivers to the hotels/resorts.
Have a great trip!