Hey Howdy Hey Megan and welcome to planDisney!
As a Girldad of three, I can totally relate to your situation as this has come up on our end as well. A lot of the information Disney collects is to simplify your reservations so you can quickly purchase the appropriate theme park tickets as well as room accommodations with the age groups appropriate for your party. Let's take a quick step back and review a few things first.
The first thing to note when you are traveling with an infant under the age of three to Walt Disney World is that they are included in the headcount for reservations but are not charged as a child over the age of three. This applies to room reservations, tickets and dining reservations.
Disney will have you set up or link a
My Disney Experience account profile for all Guests on the reservation however those under the age of 18 will have their parents as the ones that are in charge of their accounts. As long as you are the one setting up the account, after your baby is born you can go in and update their birthday accordingly for their My Disney Experience account. This technicality only matters when they are age three as they are now required to have park tickets and all the other things. So long story short, I would put down a tentative birthday with the expectation that you can change it.
The other thing I wanted to let you know about when traveling with an infant to the parks is the benefit of having
baby care centers in all four theme parks. These locations are so convenient to have a place to feed your baby in a more comfortable and quieter place than is available in the general park areas. You also have the option to purchase things like diapers, wipes and things you may have forgotten at home or in your room so you can avoid the long trip back and pick those things up in the parks. They are really convenient places to visit in the parks when traveling with little ones.
I hope this information helped set your mind at ease about the My Disney Experience account. If you have any further questions please feel free to reach out, we would be happy to help!
Have a Magical Day,
Nick