My DS turned 4 on our trip. We spent the day of his birthday at MK. We got him the pin at Town Hall. I was kind of dissapointed in the fact that not one CM noticed his pin or wished him Happy Birthday on their own! I had to tip off a CM at the Indy Speedway to please go back to his car(he was with Daddy) and tell him Happy Birthday which he cheerfully did do.
Never-the-less, our little boy tells everyone, everywhere we go that he had his birthday at WDW so it didn't matter to him at all that he didn't get more special treatment. My point is, not to get a child's hopes up about any extras. It WILL be a special memory for them. In defense of Disney, it was quite crowded when we were there. We had dinner at the Plaza Restaurant and they brought him a nice cupcake with a candle(we made sure they knew about the birthday).
Make your own magic if necessary...the rest will be icing on the cake, so to speak.