I would go to the outlet mall. It's a taxi ride (or short drive if you have a car) offsite - maybe 15 min depending on where your resort is.
Orlando Premium Outlets
8200 Vineland Avenue
Orlando, FL 32821
(407) 238-7787
Kids stores I've shopped at:
Carter's
Gymboree
Hartstrings
Oshkosh
Polo Ralph Lauren Children
(there are more stores, but these are the ones I normally look through)
I bought a lot of stuff there while on vacation while I was expecting DS, and also for my sister when she was expecting. I did take an extra suitcase!
There is also a Disney outlet store there, where you can get some baby Disney branded items.
This is all mostly clothing related stuff. I'm not sure if you'd be looking to take strollers, car seats, etc back - but if so, Babiers R Us and Toys R Us may be best. You can also find a lot of baby items at Target (I normally shop the clearance racks there, but regular prices will seem very good to you).
I've bought DS some baby items in the UK while we were travelling there. I ran out of diapers and just needed a couple warmer items. I could not believe how expensive it all was (esp. because the exchange rate was about 2-1 then).
Have fun!