Emma’s abandonment is rather unique in that she never knew her parents at all. In Neverland (traditionally) the Lost Boys don’t even remember what a mother is. That’s how they are alike, they’ve never known their mothers. Hook, Rumple and Bae for example all knew their parents but were left by them at different ages.
If I had to guess, I would say Emma heard them because of her uniquness but also because Pan wanted her to.
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"He was a lot of things to me" "The only conclusion was love"