Thank you to everyone for the input. A lot of what has been said are the same thoughts that have been going through my mind.
My exact situation will be having a 5-7 week old for a 2 night, 1 day trip to WDW the first week of Dec. This is not as busy as many other times of the year, nor is it as hot. Also the Grandparents will be there along with her Uncle, Aunt and 14 month old cousin.
With the extra help we would have, being there at a slower/cooler time of the year, and only being there for 2 nights we are hoping to be able to pull this off. It will be my Nephew's first trip to WDW, and it would be very special if we were able to make it our daughter's first trip as well. But we do have our concerns.