The Deep End of the Ocean by: Jacquelyn Mitchard

Beth is a mother of 3 children. Life is fairly good. When Beth goes to her high school reunion she takes her three kids, Vincent-7, Ben-3, and Kerry-baby. As Beth is checking in Ben is kidnapped. She turned her back for a second and her son is missing. 4 hours pass and no Ben. 4 days pass and no Ben.  4 months pass and no Ben. 4 years pass and no Ben. It seems that Ben will never be found again. The book takes you through Beth and Vincent's most inner feelings and what they have to go through to come to terms with Ben being gone. Then 9 years later Ben reappears. He has no idea he was kidnapped. And the whole family is reunited. But they aren't really a family.
This book is defiantly going to find a place on my book shelf some time soon. It is a must read and a must own. The movie was also pretty good. Though I watched it before I read the book so I can't remember how accurate it is.