It's called the 'Bait Boy' prank. Dress up a child sized doll in a costume holding a bag, and bring him to different houses on Halloween.
Meet Bait Boy Spiderman - the guy places him on the doorsteps, rings the bell and waits. The unknowing homeowner is much too happy to give out the candy to the little boy who doesn't move or speak. His dad uses the excuse of 'he's shy' or he's deaf' to cover for him.
After the candy is in the bag, dad picks up the boy and walks away - leaving the neighbor with an extremely puzzled expression.