Actually, this event occurred before the Halloween which is detailed most thoroughly in the novel. The dating is important to the chronology of the story.
Some children—Scout swears she was not among them, leading us to suspect that maybe she was: "I deny having taken part in such a thing," she writes— crept barefoot into the home of the maiden sisters, Misses Tutti and Frutti Barber, who were old women and hard of hearing. These children moved all the furniture in the house into the cellar. (The Barber sisters were notable as the only people in Maycomb to have a cellar.)
When Mr. Tate is called on to take action, he sends out his dogs to sniff the feet of Maycomb's children to find the culprits. This leads every child to put on shoes. This sounds like a bit of a tall tale (why would every child put on shoes if only a few were guilty?) but it serves to explain to why the adults in Maycomb felt the need to regulate Halloween for the first time:
So the Maycomb ladies said things would be different this year. The high-school auditorium would be open, there would be a pageant for the grown-ups; apple-bobbing, taffy-pulling, pinning the tail on the donkey for the children. There would also be a prize of twenty-five cents for the best Halloween costume, created by the wearer.
This organizing of Halloween events leads to Scout becoming a ham for the school pageant.