When the narrator reviews old photos she claims to see the missing part of herself. What is the missing part?

The missing part of the narrator is innocence or the naturalness that one possesses as a child. Even in the photos where she appears moving or unkempt, the narrator is easily able to identify her childhood self. However, she believes that part of her has been lost, and because it is locked away somewhere, she has been left numb and detached.