Seeing "Olive" as a child made me wonder if Peter and Olivia knew each other from childhood, as we know Walter tested things on Peter- and again, it could be a pointer to the brother/sister theory, I guess. However, her intense jelousy over his blossoming friendship with Rachel surely isn't natural for a sister to feel, if we are to believe that theory. Perhaps they were also childhood friends? It's possible they don't remember, as Nick Lain (sp?) asked Olivia if she remembered him, and she said she didn't. So perhaps, at some point, Peter and Olivia will remember each other from childhood- or one of them will.