Hi, Alison!
You're going to have such a wonderful family vacation together in Walt Disney World this March! How exciting!
Regarding Character Dining Experiences, you should let Disney Dining know that you are a party of
six. This will ensure that you have a table which can accommodate the baby's high chair. Let them know the baby's age when you book, too. If you are the Disney Dining Plan, they wouldn't be able to count the littlest member of your family anyway, so that's fine, too.
If you'd like to check out a complete listing of
Character Dining Experiences at Walt Disney World.com, I provided you with the link. So many to choose from! :-)
Have a wonderful trip! Bring lots of room on your camera's memory stick; you're going to need it! :-)