Most Amish kids probably don't trick-or-treat for Halloween, let alone dress up in a costume. However, I have always let my kids participate. In case I hadn't mentioned it before, my scholars attend public school and not Amish School. Most of the classrooms always have parties. We also have a few English neighbors, such as Bunny that always invite the kids to come and trick-or-treat at their place.
I don't buy costumes or even sew them, but I tell the children each year if they want to come up with a costume, that is just fine by Jacob and me. Mostly, they dress like hobos, or old people, or fat people. They might put a little mud on their face, or some talcum powder in their hair, or stuff a pillow under their shirts. A few times the boys have borrowed a nightdress of mine and usually the girls will dress old, like Mommie. It doesn't really matter, because mostly, they just have fun.
Bunny says living out in the countryside, they don't see too many trick-or-treaters so when my children show up at their door with their empty pillowcases, she usually fills them right up with candy bars, popcorn balls and whatnot.
This year Bunny had on a long red dress and a red cape and some devil ears. It was a good thing she wore the same amount of make up she normally does or else she might have scare't the younger ones.