I too, I must confess, take great delight in making the little ones (but not the wee ones, under 10 or so) run home for clean shorts. A trait inherited from my demented mother, I think.
[sub]Actually, she’s a lot like Rosanne, 'round Hallowe’en, now I think of it.[/sub]
My most successful garb for this is simply a black cloak, with an oversized (and handmade, might I add) hood. I don this, then adorn my noggin with the largest pumkin I can find, carved out in wicked fashion, hence the oversized hood. I blacken my face and put those tiny little glowsticks in the pumpkin’s eyes and mouth, making the whole deal look like the scarecrows everyone loves to have in front of the house, at this time o’ year.
Using the time honored methods described by welby, I wait until they’ve gotten their loot, then jump up wailing and shouting, followed by much chuckling and giggling as they scamper for the curb.
Good on ya, welby, and here’s to a less painful holiday, next year. 
For a bit of variation, I’ll sometimes take advantage of thier curiosity, and wait 'till they’ve leaned in real close to me, checking out the “scarecrow” and give 'em a “Booga booga!” Though fortunately, I’ve never been taken down by a groin kick. Yet.
[sub]The trick, y’see, is to squint your eyes, so all they can see is the glowstick, and the makeup on yer eyelids hides the truth, until you give 'em a gotcha.[/sub]