Hi, Melanie!
Wow! You must be so excited for your upcoming trip to Walt Disney World! It's right around the corner!
I would take your little prince on
Toy Story Midway Mania! and into
Muppet*Vision 3D, and plop those 3D glasses onto his face at the latest moment possible. Once the 3D action begins, you might just be able to put the glasses on him in such a way that he barely even notices (much like sunglasses on a sunny day). He may be so mesmerized with the sights and sounds around him that the glasses become a non-issue.
If, however, he simply will not tolerate the glasses, I don't think you'll have a problem, either. I've taken those 3D glasses off from time to time, just to see how different it looks without them, and everything is perfectly visible. There will be what looks like a super-imposed copy of what you're seeing (in double or triple form) but it's very faint. On Toy Story, for example, there is a lot of movement, so he may be very intrigued by the action, too. In Muppet*Vision, the storyline and soundtrack will probably be enough to make him leave those glasses on.
The glasses' arms are tight enough, too, that they will probably stay on his little face just fine. Give it a try! (And be ready to take a photo of the little man in his glasses, should he choose to leave them on. What an adorable shot!)
Send more questions as you think of them, Melanie! We love to help!