IGTD, I hope I'm not too late, I'm not sure when you leave for your trip!
I love all of the above ideas and I have one more...one of my friends would purchase postcards from every place they visited during their trip and she would write (her daughter was too young to write at the time) what they did there, what they learned, etc. At the end of the trip, she would punch a hole in the corner of each postcard and put a ring through it, and it made for a great, inexpensive souvenir, and also a journal.
Maybe you could use that idea and do something similar, but put a little more focus on the education? Perhaps a postcard from each country in EPCOT in addition to the passport, etc. You could have him learn something unique about each country and he could write about that.