It was decided that children had to be more supervised on Halloween because there had been mayhem the year before when a practical joke got out of hand.  As a result, the ladies organize a pageant and activities for the town.  This is significant because it is when walking home from this pageant that Scout and Jem are attacked by Bob Ewell.

The year before, Maycomb changed its Halloween celebration practices.

Halloween in Maycomb was a completely unorganized affair. Each child did what he wanted to do, with assistance from other children if there was anything to be moved, such as placing a light buggy on top of the livery stable. (ch 27)

 The year before, though, “some wicked children” had snuck into the home of the two Miss Barbers, who were deaf.  They collected all of the furniture and hid it in the basement.  Sherriff Tate was called, and brought in bloodhounds from ten miles away.

The ladies organize the festivities.

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… (ch 27)

As a result of this, Scout gets the part of the ham in the pageant and Jem has to escort her because Atticus is too tired.  On their way back, they get attacked by Bob Ewell and Boo Radley saves them.

The Halloween story is useful for describing how laid back the people of Maycomb are about their children.  This foreshadows trouble with Jem and Scout as well on Halloween.