How does the author use foreshadowing in Flowers in the Attic?

In Part II, as foreshadowed in previous chapters, Cathy and Chris's sexuality is beginning to blossom like it would for any children their age. Cathy begins exploring her changing body by staring at it in a mirror and Chris comes down. Chris is fascinated with Cathy's body too because it is the only female form, besides Carrie's, that is available to him. If Chris had access to other girls his age or to movies and magazines, he would not be interested in Cathy. However, Cathy is the only girl he has access to, causing a situation in which he has become fascinated with her.