Hi, Rebecca! I don't know much about your son, but with kids of my own who are 8 and 12, DisneyQuest would be high on both of their lists of fun things to do for their birthdays. Located at Downtown Disney, you'll find five floors of virtual reality games, classic video games, and and other assorted interactive video activities.
You might also check out some of the behind the scenes tours. Among the ones that would be really cool to do with kids this age is the Family Magic Tour. Built around a scavenger hunt theme, you'll discover stuff about the Magic Kingdom you've never heard before, and possibly run into a favorite character. You'll find more information on this - and some other backstage tours - by clicking
Walt Disney World Special Events and Tours.
There are some neat dining experiences you could consider for a special birthday dinner. The Sci Fi Dine In brings you to the scene of a drive in movie theater from back in the day, sitting in your car, grabbing a burger, and enjoying the film - or in this case, movie clips. Check out T-Rex Restaurant in Downtown Disney, where you'll dine among the dinosaurs. It's really a great experience.
Another thing that would be great fun is a visit to Splitsville, the recently opened bowling alley on Disney property. It takes this fun family activity and kicks it up a notch with more intimate lane spaces, amazing food, and just a special flair.
Have a wonderful time on your upcoming vacation!