Maybe to avoid charging admission as crowds get bigger, just ask the folks wanting in if they can sing of few bars of something. No song, no admission. There's a Scots neighbor of mine who always used to ask the kids to sing a song when they went trick or treating at her house--she told them that's how they do it in Scotland (is it?). My kids were ready--and she gave bigger candies to those who were up for the game.

SRS