I have a co-worker who will be travelling to WDW with her family, including her 12 month old daughter. This will be the first time they are down there with a baby. (They are staying on-property).
I told her I would post this here, and let everyone give suggestions on "Must Have's", "Don't Forget's", and other "Baby Tips".
Thanks!
My DSIS is taking her 12mos old w/ us this year. Bring or
rent a stroller & go (not a park stroller, those are hard)
Little fans w/ extra batteries. Get a few fans, b/c they tend to break. You can rig up the cheap ones from the dollar tree to velcro security ties from the dollar tree.
Velcro security ties are the best invention in the world.

You can rig up so many things w/ them. ie. tshirt sleeves (embelish w/ a bow), sippy cups, pacifiers, secure down a poncho on stroller when in rides incase of rain, secure wet clothes from rides to stroller to dry out (or pee pee bloomers...been there)
Have diapers delivered to hotel if you fly out there (gardengrocer.com or
amazon)
Take breaks when you need to. Get some icecream or treat. Babies love sharing food in the shade. You can't keep crazy pace w/ little ones, but you can have a lot of family fun.
I've taken my 2 at all ages & loved it each time. You can take babies on a lot of rides (within reason). Don't think you will be parked on a bench the whole time. You can do parent swap too. My DD loved the Haunted Mansion when she was 1yr old, but hated it when she was 2yr old. So DS & DH hit the Mansion & we hit Small World.
You don't stop living your life when you have a little one. Some people drive me nuts when they act like "Oh, you can't take one that small to Disney. It is just a waste of money." Disney has lots of things to do w/ small ones, even in the heat.
Parent swap Test Track & take the little one inside one of the Innovations buildings to play. Swap w/ DH & let him play w/ little one in Innovations. DD likes sitting under the track waiting & listening to the cars pass.