Answer:
The detail, "And someone gave little Davy Hutchinson a few pebbles", contributes to the text because his mother was the one being stoned, but the person who gave him some pebbles was suggesting that he needed to start participating at a young age, just as everyone else did.
I'm pretty sure it is Theme.
Theme is the central topic of the text. passage, story, or anything else. So it may possibly also be the same for the underlying meaning and universal truth...but again, I am not sure.
