The Face on the Milk Carton, by Caroline B. Cooney
I read the short content of this book on the back cover:
"No one ever really paid close attention to the faces of the missing children on the milk cartons. But as Janie Johnson glanced at the face of the ordinary little girl with her hair in tight pigtails, wearing a dress with a narrow white collar--a three-year-old who had been kidnapped twelve years before from a shopping mall in New Jersey--she felt overcome with shock. She recognized that little girl--it was she. How could it possibly be true?"
Isn't that the most intriguing short content you ever read?! I simply had to read the book after that.
Janie can't believe that her loving parents kidnapped her, but as she begins to piece things together, nothing makes sense. Something is terribly wrong. Are Mr. and Mrs. Johnson really Janie's parents? And if not, who is Janie Johnson, and what really happened?
As a child I always imagined that I had been adopted... so this premise appealed to me. A good read and, if kids like it, there are several more titles in the series to keep 'em reading!