Since you are travelling with a baby this may not be feasible but we try to get 8 am. breakfast reservations inside the park, particularly Magic Kingdom and Epcot. If anyone in your party is interested in Soarin or Test Track, Garden Grill is a good place to get breakfast. It also has characters. We get there at 8, eat, then walk downstairs to get on Soarin, They'll usually let you on early so you can then head over to Test Track. Frees you up to do other things, even take a mid day break. Not sure how the new Ratatouille ride will impact this. For Magic Kingdom, you can catch 7 Dwarfs Mine Train, and Peter Pan. There's a lot to be said for getting in the park before it's officially open, if for no other reason to move and breathe. Be Our Guest is great and it's a quick service credit as opposed to table service. Garden Grill is table service but only 1 credit and you get characters.
As someone said, read, read, read and have a spread sheet or list. I also look at hours from previous months and years. Also know that there are events which either open or close certain parks early. There are lots of tips on how to maximize your time, ability to get around the parks and attractions, as well as your dining credits. For instance, you can get breakfast, lunch or dinner at 2 locations (only Hollywood and Vine is open for breakfast) inside Hollywood Studios that also gets you a preferred seating for Fantasmic! and Hollywood and Vine has characters as well for 1 table service credit.
In my opinion, the hardest to get reservations are: (for our party of 6)
Any pre park opening breakfasts, especially those that give you an attraction advantage
Cinderella's Royal Table dinner (2 credits)
Storybook Dining at Artist Point with Snow White
Sci-Fi Diner
Beaches and Cream
50s Prime Time Cafe
O'Hanas can be difficult
Be Our Guest dinner (2 credits)
California Grill brunch (2 credits)
Trattoria al Forno breakfast ( you can get it but sometimes the times aren't ideal)
There are others, but these are ones and I've probably missed a couple, which are in or near parks. Most of these can be reserved if you are up and ready at 180 days. The morning of my reservation date the website was glitchy and I could only get Storybook at 8 PM and Sci-Fi at 4:00 but I'll keep trying. I have been able to move 2 of our pre park opening bookings up a little. Don't panic though. Discuss your must dos and go for them first.
Edit to add: Mickey's Very Merry Christmas Party was held Sunday, Tuesday, Thursday and Friday on the same week last year. That will leave only Monday and Wednesday to get a full day at the Magic Kingdom (the 30th and 2nd) if that is the same this year. If you are interested in the fireworks, plus, looking at historical dates, Wednesday usually has evening Extra Magic hours, so if you are planning a meal at the Magic Kingdom this is something to consider. What would work for my family is pre park opening breakfast at Be Our Guest, jump on a few time consuming attractions early, either through early morning advantage or fast passes, then take a mid day break and come back for late afternoon/ evening fun.