My DD was 7 months last year & will be 19 months this year when we go. Some things I did...
*Pack wipes EVERYWHERE. I had them in a few different carry ons and then a tub in my luggage and some more stashed somewhere else. DItto for diapers and a change of clothes (or two -- DD had a huge blowout on the way to the airport when we were leaving and then AGAIN that night at the parks).
*they will let you bring unopened juice/milk for kids, and bottles through security (at least as of a year ago) I put that stuff in a separate gallon size zip lock bag and took it out of our big bag to go through security. They didn't give me any problems. Ditto for baby food jars. And the more organized you are with stuff like that at security, the better! I had meds in one bag (i carry an epi pen for DS & DD and benadryl always), my "travel size items" in another, and the juice/food in another.
*I put baby food, diapers, snacks, sippy cups in a small suitcase we checked. We used most of it while we were there, and then had a suitcase free for the souvenirs we brough back.
*don't forget tylenol/motrin, benadryl if you have any allergy concerns, & a small first aid kit.
*I packed a change of clothes & pjs for everyone in each suitcase. That way if one got lost, we had at least a day's worth of clothes for whoever's wasn't there.
*I choose a blanket & one or two special loveys to bring (making sure I have a duplicate at home if one is THE one)
*bring books for the plane -- a new one or two is always a good idea. I might bring our portable DVD player or laptop so she can watch a movie on the plane.
*Bibsters and table toppers are awesome additions at restaurants
*bring jackets. Mornings and evenings are chilly and it often gets much warmer during the day (we go in Dec. & had one week where it was mostly 85* and then last year mostly 70ish* w/ very chilly evenings)
*depending on where you are staying, you might want to pack a small thing of dish liquid to wash cups/bottles.
HAVE FUN & try not to stress. The great thing about Disney is you can buy pretty much anything you've forgotten!!!