Hi Robyn,
I see this is your first post. Welcome to the board! This is a great place to come to for information on how to get the most out of your trip, especially with little ones in tow. We went with our ds when he was 13 months and again at 17 months and will be there again in January also.
I was amazed at the difference just a few months made on our last trip. Our first trip he was frightened of loud noises so we had to skip a lot of the shows, but our second trip he loved everything, including the character greets. Every baby is different though - my suggestion is if you want to try one of the 3-D shows like Mickey's Philharmagic (@MK) try to be one of the first entering the theater so that you're near the exit. That way if she decides she doesn't like it you can get up and leave (Boy do I wish we had done that, LOL).
As far as the weather goes, you can get a 10-day forecast on
www.weather.com - that's usually what I do. I imagine that being from Chicago you will find the weather to be very tolerable even if it's a little on the chilly side though. I went in December a few years ago and it was unseasonably cold that year so this year I will probably be bringing a few pairs of long pants and a couple of fleece shirts just in case. Hopefully the weather will be pretty nice.
Will you be on property? Disney is starting a new "extra magic hour" program that will allow guests who are staying on property to come in one hour early and then the park will stay open 3-hrs late as well.
rDefinitely use the Baby Care Centers - they have nice cushy changing tables and high chairs with trays just like the ones you use at home. They also have a mothers nursing room if you want a private and quiet place to nurse baby (although you can do this discretely just about anywhere in the parks if you want to). There is baby food available for purchase there if you should need it as well as a few other sundry baby supplies like diapers and binky leashes. It's just a nice quiet place to go and relax for a few minutes if you need to. All the regular restrooms (including the mens) have changing tables too.
If you and your dh want to go on a ride with a height restriction then you can get a "rider swap" pass - just ask the CM at the ride entrace and they will give you a pass and explain how it works for that ride.
Hope that is helpful! Another site I find very helpful is
www.allearsnet.com.
Have a magical trip!
Cheryl