I've always just mentioned my DDs birthday to the CM when we make our reservation. Her birthday happens to fall right around the
free dining time, so lucky her, she's about to have her 3rd WDW birthday in a row. When we checked in the last 2 years, they ask who her favorite character is and then one random day during our trip we come back to the room to find balloons and a card with an autographed picture of a character. Sometimes it is the favorite, sometimes not. This happened with my other DD too last year for her birthday. The buttons you just pick up at Guest Relations at any park or City Hall in the MK, sometimes they have them at the turnstiles.