How does detail "and someone have little Davy Hutchinson a few pebbles" contribute to the text

this means that little Davy is going to contribute to the stoning of his mother;

Explanation:

This contributes to the twisted irony of the situation, that the tradition is more important than family ties.

the tradition is continuing / being taught to the younger generation;

This means that little Davie is encouraged to stone, murder, his own mother. This contributes to the twisted irony of the situation.