I think this tweet thread from last year says it all, really:
My standard response when a younger child does the “Trick or Treat?” thing to me is to say:
“I don’t know; which one do you want me to do to you?”
If I say it loudly enough, it’s generally enough to have a Helicopter Parent come steaming up to the door and snatch Their Precious Child away from me. Then I throw gumballs at their retreating figures.