We had never heard of sensory processing disorder at that point, and didn't know that the sight of all those kids, especially kids in costume, and the unpredictable volume of 20 excited fairies and monsters.
I didn't make him keep the hood up, and he hung back from the large group, heading to the door as the last kid left. He did okay, happy about getting candy, and only breaking down when the group shouted trick or treat for a camera.
This year, though, we're talking about Halloween, what happens, what is fun, and letting him decide if he wants to take part. So far, he has said no, and despite my own love of trick or treating, I won't ever force him again.