My DD turned 7 on our last trip. We contacted the front desk and asked if they do anything special for birthdays. They delivered helium balloons and a card autographed by her favorite princess while we were at the parks.
We had breakfast at Cindy's and got a birthday badge at City Hall in MK which had "It's my birthday today" and the CM had her talk to Goofy on the phone while we were there and he wished her a Happy Birthday. All the CM's wished her a happy birthday while we were in line and such that day.
We ended her day with a birthday illuminations cruise. They had balloons, streamers, sign that said "Happy Birthday" with a lovely birthday cake and sodas for the cruise to watch Reflections of Earth Illuminations. People in Epcot sang "Happy Birthday" to her, too from the shore! She thought that was so cool!
Make sure you bring wrapping paper for presents with you if you don't wrap them at home; I forgot that and had to wrap her presents in WDW bags! They worked!!!!!