For the past two years, I've put Lego displays in our front window on Halloween night for trick-or-treaters to see as they approach our front door. The displays always seem to surprise our young guests (and sometimes the parents, too) -- maybe because you don't expect to see Lego in a Halloween display. (The people next door have about a dozen 6-foot-wide inflatables in their yard. So that's, I guess, normal.)
Anyway, I want to preface this by saying I threw this display together in less than an hour. I already had the house built. I just put some baseplates together, added some trees and leaves, then dug through my collection of minifigs, searching for ones that looked like they were wearing a semi-typical Halloween costumes. Then I searched for things for them to carry their candy in (buckets, backpacks, satchels), added colorful 1x1 rounds for candy, and set it all up in the front window.
In order for the display to be seen, I had to shine several lamps on it, from the side and from behind. It was hard to get a good photo of it. But afterwards, I took some shots with good lighting so you can see what I did. I'm not saying this is one of my best builds (not by a long shot!) but I thought it might be something kids could build around Halloween. Just about any minfig from the collector's series (those ones you get for $2.99 in the mystery bags) would make a good "costumed kid." Give it a try! It's a quick & easy build.