Here are a couple of books you could try (I've read the first one myself and it's pretty interesting):
1. Who was Walt Disney?: By Whitney Stewart and Nancy Harrison. It talks about how Walt Disney always loved to entertain people, which more often than not invariably landed him into trouble. For instance, once he painted pictures with tar on the walls of his family's white house. His was a family which was not very well-off, and some of his happiest times were childhood years spent living on a farm in Missouri. The black and white illustrations throughout the book add to the charm.
2. Walt Disney: An American Original: By Bob Thomas. This book talks about the American hero Walt Disney, who was the creator of Mickey Mouse, and who changed the face of American culture. The book is the result of extensive years of research by the author and is based on private papers and letters of the protagonist of the story. It makes for an engaging read which tells the story of an unschooled cartoonist from Kansas city who went bankrupt with his first movie venture but ultimately became the genius who produced unmatched works of animation.
3. Walt Disney: The Biography: Can't say much about this but have heard that it is a detailed re-construction of the events of the animation great's life and works.