Hi Amanda! It's always nice to meet a fellow homeschool family! As you know, everything can be a learning experience and Disney World is full of them!
Here is a link to the
individual enrollment site for the YES classes. I did look and it seems that the "How Things Move" class is the only one offered for your son's age. You can also call 877-WD-YOUTH if the website isn't clear.
Another thing we love are the passports at Epcot's World Showcase pavilions. You can buy them at an Epcot gift shop for around $10. You take it to the Kidcot Fun Stops around the World Showcase Pavilion and your son can have it stamped and signed in each language by cast members from that country. There are also some stickers he can put on each country's page.
The American Adventure show at the American Pavilion in Epcot is a great and entertaining introduction to how we became a country. There are other movies around the World Showcase, but a 5 year-old may not find them all that interesting...but I sure do! Living With the Land in the Land pavilion at Epcot is a great educational ride about agriculture. Also, in Epcot's Future World are the Innoventions pavilions. They are full of educational and technological activities and are constantly changing.
The Magic Kingdom has the Hall of Presidents and Carousel of Progress.
At Animal Kingdom, take the Wildlife Express Train back to Rafiki's Planet Watch. There is a petting zoo, habitat wildlife trail, and sometimes you can even see them examine the animals through a glass window. Just get there early for that! They usually do the check-ups before lunch time.
There is so much to do at Disney World! My boys both love all of these things! Please let me know if I can answer any other questions!