Would rather take an infant than a toddler or kid any day! When we started ours were 18 months and 6 months (they are a year apart). WDW is great for nursing and baby care in general, all bathrooms have changing stations, baby care centers are priceless and most attractions baby can do with you. We have 4 children and one due in September so I have taken babies at every age here are my suggestions:
Get a good carrier or wrap, please not a Bijorn, google the health issues they cause. We liked the Ergo and a mesh UVA/UVB wrap that is light weight and can do different holds. Park the stroller, wear the baby, much easier in the different lands.
Make sure your baby is out of the sun with a stroller shade, we have a sun shade attachment the completely covers the child but allows them to see out.
Get a stroller fan, oddly the Mickey one sold in the parks is cheaper and IMHO better than Babies R Us
Pack an extra onsie
Get the rain cover that fits your stroller, put it on when you open the stroller and roll it back. Trust me much easier to roll it on in place than fighting with it while getting drenched! Also line your stroller with a hotel towel, might keep your stroller cleaner and can be used for anything and everything. The poncho clipped on never seems to work, especially with any sort of rain
If baby is eating solids have goldfish or the like handy.
Over pack diapers
Test sunscreen on baby before you leave
Really go over your diaper bag for the parks and see what is needed. Less is less to carry!
Sure you might not get done what you used too, but you don't get done with anything like you used now that baby is here
Blessings for you and baby