First off, welcome to the Moms Panel, Patricia! There are so many ways to celebrate and make your son feel special at Disney on his birthday. Let me start with a few suggestions. When you make any of your Advance Dining Reservations, be sure to mention that you are celebrating a birthday. You never know what surprise you may get at the restaurants. If you are staying at a Walt Disney World Resort, be sure to mention the birthday at check-in. Your son will be given a birthday button to wear. I bet he smiles from EAR to EAR when he hears how many people will wish him a "Happy Birthday" along the way. If you are not staying at a Disney Resort, you can also request these buttons at any Guest Relations window in any of the 4 Parks. Cast Member keep their eyes open for those pins. I've warned you!
For your group, I would strongly consider booking a VIP fireworks cruise to view Illuminations at Epcot or Wishes at Magic Kingdom. You can even have the boat decorated and order a birthday cake! Although
this link says the cruise is for up to 10 people, they will go up to a maximum of 12 people if you have a mix of adults and kids. Be sure to mention this if you decide to book.
I hope you son has an amazing birthday, and I wish you a MAGICAL vacation!