In literature, "loss of innocence" means that a character has ended her childhood and become an adult. This can happen in a variety of ways, and it can be symbolized throughout the text. One such example occurs in "Alice in Wonderland" when Alice struggles with boredom or with being an inconvenient size. Loss of innocence is also sometimes referred to as coming of age.
Innocence is related to guiltlessness or lack of knowledge. In literature, a character may lose his innocence by becoming aware of the world around him or by doing something that evokes guilt.
For instance, in "The Catcher in the Rye," a classic coming-of-age novel, the protagonist Holden Caulfield is in the midst of losing his innocence. He has been expelled from four schools, he sees most people as "phonies," and he is dealing with the death of his brother. However, he is not ready to consider himself an adult, and the book frequently deals with the theme of innocence. Caulfield wants to protect the innocence of children, which is symbolic of his need to protect his own childhood or innocence. At the end of the book, he resolves his emotional trouble, pledges to do well at his next school and expresses optimism. This symbolizes his acceptance of his looming adulthood and his symbolic coming of age or loss of innocence.