What is the theme in The Face on the Milk Carton by Caroline B. Cooney?

The theme of fantasy versus reality is explored throughout the novel by Janie's recurring thoughts and images. A distinction is made between daydreams and daymares. Janie refers to daydreams as something over which she has control, such as her fantasies about having kids named Denim and Lace. Her daymares, on the other hand, are uncontrollable images that play out in her mind. She often has no idea as to their meaning and becomes increasingly worried about whether or not these are true. Are they memories from her past or just scenes that her mind has created as a result of seeing the picture on the milk carton?