2) In Peter Pan, the hidden kiss is located in the corner of the mouth, where the lip begins to turn out. It could just be a term for that area of the mouth. Or, maybe Mrs. Darling's "hidden kiss" is there, because that is the area where her facial expression changes… ruining her façade.
-If anyone is especially interested in this term, check out literary discussions that compare the metaphors of Mrs. Darlings hidden kiss, with Peter Pan and Wendy. Very poetical stuff!