Hi Amanda!
Celebrating a birthday at Walt Disney World is a very unique experience. There are several things you can do to make their birthdays special. First I would start with a character breakfast at Chef Mickey's. It is a lively restaurant where you will meet Mickey, Minnie, Goofy, Pluto and Donald. Bring birthday cards for the characters to sign, it makes for a great souvenir.
When you make a dining reservation you can order a birthday cake for your table. Birthday cakes can be pre-ordered when you make your dining reservation.
You can bring some decorations from home to decorate your room or you can order something special from the Disney florist. I have linked you to their website to take a look. Click
here to visit the Disney Florist.
When you arrive at the parks be sure to stop in at guest services and pick up some free Happy Birthday buttons. The will be stopped by several cast members who will with them Happy Birthday.
Have a magical vacation!