Hi Candice,
I can't think of a better place to celebrate a birthday than Disney World!
If you're staying at a Disney Resort, be sure to pick up a "Happy Birthday" button for your son to wear. If not, you can pick up one at any Guest Relations location in any of the theme or water parks. That will attract attention from Cast Members during your trip.
Chef Mickey's is awesome! I love the breakfast and dinner buffets there. Be sure to mention that you'll be celebrating your son's birthday when you make your reservations.
They typically bring out a cupcake with a candle in it. They also brought out a card for my son signed by all of the characters. The waiter didn't sing, he just delivered the cupcake and the card. As far as the characters coming over to sing, the fur characters don't talk so they can't come over to sing (they have to save their voices for their TV appearances). They will be happy to pose for pictures when they come to your table but don't usually come over as a group - just one at a time. They have somewhat of an order in which they visit the tables. If the cupcake is brought out about the time one of the characters is near your table, they may join the celebration in some way. While nothing is guaranteed, you never know what magical moment will spontaneously happen.
If for some reason you can't get into Chef Mickey's, try the
Cape May Breakfast Buffet (characters appear only at breakfast) at Disney's Beach Club Resort or
Best Friends Breakfast featuring Lilo & Stitch at 'Ohana at the Polynesian Resort. Both of these are great options as well.
Please feel free to visit with any other planning questions. We're thrilled to assist you!
Wishing your son minnie magical birthday memories :-) Allison