That's wonderful that your son and your family will be able to celebrate his birthday at DLR! Make-a-Wish is such an inspiring program! My family will be there at the same time and my DD will be turning 7. How old will your son be? Is he into Star Wars? There's a great thread for how to get picked to go up on stage during the Jedi Training Academy. There's lots of inexpensive ways to make a birthday special. Get a birthday button at Town Hall, ask the conductor to ride up front or if you could get a ride on the Lilly Belle, make reservations for Pat E. Cake's for a birthday celebration with cake making and games with Mickey and Minnie.
There were several threads going about the planners who do the gift baskets, food surprises (like cookies and milk), and baloons a couple of weeks ago. I'll see if I can find them. If not, don't hesitate to start your own thread and asking about them.
So glad you're joining us here on the DISBoards to help plan your trip. It's a really nice group of people and I think you'll get lots of excellent ideas.