What are the differences in tone between the book and the movie?

The Face on the Milk Carton tells the story of Janie Johnson, a teenager who discovers, through a missing child photo on a milk carton, that she was kidnapped when she was small. The parents who raised her didn't know that Janie was stolen; they believed she was the child of their estranged daughter, so they raised her as their own. The news that Janie was kidnapped and does not legally belong to them is devastating to everyone involved.
The novel tells Janie's story in a serious and somber tone. She still deals with light, teenage issues, but the heavy parts of the story are clearly emphasized. In the movie adaptation, the tone is lighter. There are more warm and fun moments than the book allows. It's obviously been adapted for a TV audience, one with a variety of ages.