Hi Samantha!
Welcome to the Disney Parks Moms Panel! First let me say a big *chEARs* on the news of your mini Minnie!! I jumped over to the Walt Disney World Resort website and started playing around with Dining Reservations,
adding someone to my My Disney Experience account, and I even went through the steps of booking a Walt Disney World Resort Hotel reservation. Here's what I found.
If you try to add your daughter to your
Friends and Family list in your My Disney Experience account, you will indeed be required to enter a "valid" birthdate. The system is letting me choose today as a birthday but not tomorrow, so to go this route you will have to wait until she's born, but literally only by a few minutes.
However, when I made both a
Dining Reservation as well as
Disney Resort Hotel reservation, I was able to get around the future birth date issue we're having. When asked to select who will be joining you from the drop-down list of all of your connected friends and family members, scroll to the bottom of the list and click "Add a Guest." Next, you'll be asked to enter your daughter's name and age, and here's where you'll come out ahead: anyone under the age of two is simply identified as an infant, and there is no date of birth verification. What's really, really awesome is that when you add her to whichever reservation you make first, her name will auto-magically be saved birthdatelessly in your Friends and Family List in your My Disney Experience profile, so it will come up in your guest list for all reservations you want to make after the first. I really like this option for you because you can go ahead and secure dining reservations for your complete party as soon as your booking window opens, and then any time after she's born you'll be able to log-in and update her profile with her actual day of birth.
Congratulations again, Samantha, and We'll See You (and your new Mouseketeer!) Real Soon!
~Kristen