leewrobe,
I celebrated my 13th birthday on the Magic its inaugural year. On the last night of our cruise was our dinner at Lumiere's; my family surprised with me a cake that had a piece of white chocolate on top with the photo of the ship on it in cocoa, along with presents. It is my understanding that if you mention the birthday to your servers and head server, they will arrange the cake for you and come out and sing happy birthday. At least this has been the case when I celebrated my 18th birthday on the Wonder in December.
Also, the servers are so wonderful and will make the day really special. Every time I saw our head server he wished me a happy birthday and always wanted to sing (side note: I hate it when they sing happy birthday to me in restaurants, so the servers said they would sing to me, but quietly, so they whispered). And at the end our debarkation breakfast, they stood in the middle of the restaurant and sang happy birthday at the top of their lungs, as we were getting ready to leave.
Disney knows how to make any occasion magical and truly wonderful!
Nicole