Hi Bo!
How exciting! Having Walt Disney World as your backdrop is certainly a magical way to announce a pregnancy. A friend of mine is visiting Disneyland Resort today and sent out a cute photo of pink Minnie ears and little pink Minnie booties with Sleeping Beauty Castle in the background to announce she is having a baby girl. Since you won't know the baby's gender that soon, you could have a pair of Mickey ears embroidered with "Baby (Last Name), Debuting in 2016" and have the mama-to-be hold them up to her tummy. You could have matching shirts made in advance announcing the pregnancy as well. Etsy is a great place to find some customized items. Are you on Pinterest? There is a plethora of pregnancy announcement ideas for you to gander at by searching "Disney Baby Announcement".
Bring a bag full of props and take multiple photos around Walt Disney World. Utilize Disney's PhotoPass service. When you get home from your vacation, you can take a look at all of the photos and choose the best one or make a photo collage.
If you would like official photos, I highly suggest booking a portrait session with
Disney's Fine Art Photography & Video. There are many locations to choose from and I'm sure the photographer can capture the exciting news with their lens. We have done a few sessions with them and are always impressed with the photos we receive.
Good luck and have a magical day!
Leslie