How does Lee use plot to emphasize the theme of "loss of innocence"?

There are many examples of the theme of lost innocence in
the various plots and sub-plots of To Kill a Mockingbird. Beginning
with the early death of their mother, Jem and Scout are left to live out their youth
with a different perspective than most children; with the emergence of Dill, another
character enters the realm of innocence lost. One of Scout's first experiences comes on
her long-awaited first day at school. The teacher, Miss Caroline, scolds and punishes
her for various reasons, leaving the budding writer desirous of never returning. A later
teacher, Miss Gates, also gives Scout reason to doubt the qualities of Maycomb's
classroom instructors.

Both of the children get an up-close
view of injustice in action when they witness the virtual entirety of the Tom Robinson
rape trial. They both come to the conclusion that Tom is innocent, and they are enraged
and saddened by the guilty verdict. The later assault on them by Bob Ewell is another
example of an incident that occurs to people much too young. Other examples include the
cementing of the knothole by Mr. Radley; the secrets told by Dolphus Raymond; the time
spent with Mrs. Dubose and the secret that she holds; and the various experiences of
Dill and his absent parents.