Kim:
What a way to celebrate a birthday!
Hands down, I would recommend spreading Epcot over a two-day period. It's a lot to cover with a grandparent and a 5-year-old. You can really enjoy each of the pavillions at the front of the park, and take in the under-appreciated Innovations East and West!
On Day 2 of Epcot, re-visit your favorites like Soarin' or TestTrack before strolling over to the World Showcase right when it opens at 11 a.m. You'll have plenty of time to enjoy the aerobatics of China and the films at France and Canada!
(And remember: register your son's birthday
here for your trip and enjoy all the special perks that come with Disney's "What Will You Celebrate?" emphasis in 2009!)
Wishing you a magical vacation!
Whitney