Remember, you need to submit a separate question for each piece of literature. I will answer the question regarding the theme of lost innocence as it pertains to Updike's "A & P."
In this story, Sammy is a youngster working in a grocery store. It is a hot summer day, and all of a sudden three young women, close to his age, enter the store clad only in bathing suits. Sammy and the young man he works with are overwhelmed at this sight: what a treat.
In his mind, Sammy takes in every detail: how the girls are different, who the "leader" is, the slipping of a bathing suit strap, the way the "leader" walks on her feet, the path they take through the store and even their tan lines. Sammy watches so intently that he makes a mistake on the order he is ringing up.
Luckily, as they approach the front of the story, the other checkout lane is filled, so the girls come to his line. However, the manager comes out and scolds the girls for their inappropriate dress, not at all an unusual expectation of that time period.
After they leave, Sammy takes a stand with the store manager, a friend of the family. He suggests they weren't doing anyone any harm. The manager reviews the store rules, but Sammy quits on the spot.
Sammy does this for himself; the girls are long gone. The manager shakes his head, though he doesn't really argue with Sammy. However, Sammy felt "ethically compelled" to speak up in the face of what he saw as unfair treatment. In that very moment, he somehow realizes that life will never be the same for him.
He has left adolescent innocence and naiveté behind, as if he has left Neverland. He will never be able to return to a time when life was so easy, so black-and-white. In this there is a loss of his innocence as he takes the step that a man might take rather than a boy, and he knows he has somehow turned one of life's "big corners."