How does the author use foreshadowing in Rubyfruit Jungle?

While walking home from school one day, Molly discovers that her friend Broccoli has a rather odd looking penis. She decided that they should make money off it by letting the school children take a look for five cents. Business is fine until a boy named Earl Stambach tells the teacher who in turn, tells the parents of Molly and Broccoli, foreshadowing trouble from the pair, and the revelation that Molly isn't her mother's child.