In case it's useful, here's what we've been doing for Halloween:

The kids aren't allowed to eat anything until it's been brought home and checked by an adult. We look up each candy on the Internet and check to see if it's listed as free of all the various things each kid is allergic to. Then we have safe candy on hand for swapping. So, for each candy that gets taken away, there's a replacement available.

I had a really had time last year *finding* safe candy. I ended up buying a bag of EnjoyLife chocolate chips and a plastic candy mold. I melted the chocolate chips in the microwave (nuke until just barely melted, then stir like crazy), then poured the melted chocoalte into the candy mold. I wrapped each piece in aluminum foil (note: don't use scissors to cut aluminum foil; it ruins the scissors), stuck on a sticker, and voila, we had cute homemade safe candies for my kiddos.

For treats to give out to other kids, usually I order a zillion glow bracelets on eBay. That way food allergies aren't a problem, and I don't need to feel guilty about giving sugar to little kids. Usually everybody is thrilled to have a glow bracelet. Last year instead we went to the Friends of the Library booksale and got a pile of books for 25 cents each and gave those out. Kids' reactions varied from, "Ohhh... books!" to "Um, do you have any candy instead?" (we did). (When I was a kid, I'd have prefered books to candy. My partner would have prefered candy to books. So we had both available, so kids of all sorts would find something they liked.)

Anyway, I don't know if anything there is useful, but that's what worked for my family last year.

-Valerie
mom, for Halloween this year, to Mr. Superdude and a large pumpkin