This scene shows that the tradition in the Lottery is having each head of a household draw a piece of paper. The text states, "The people had done it so many times that they only half listened to the directions: most of them were quiet, wetting their lips, not looking around." Throughout the story "The Lottery," their tradition of drawing names has been done for a very long time and nothing will change that.
The children gathering the rocks foreshadows something bad because at the end of the story, Tessie gets stoned using those same rocks. The story says, "Bobby Martin had already stuffed his pockets full of stones, and the other boys soon followed his example, selecting the smoothest and roundest stones." This textual evidence shows that they were gathering specific stones for the stoning.
Shirley Jackson creates the mood of nervousness at this point of the story by having the villagers wait for the lottery drawing to begin. The text states, "A sudden hush fell on the crowd as Mr. Summers cleared his throat and looked at the list." This quote above shows people were nervous and anxious about the lottery getting started and having to draw the slips of paper.