the equivalent for son in my language is pretty unisex when used in 2nd person. you wouldn't talk about your daughter referring to her as son, but you'd say to her face 'son, could you please..' that sort of thing. but you won't call all girls son, only the ones you're intimate with, and some dont ever call a girl son, some always do. did that make any sense?
anyway, last week a friend told me how much she liked being called daughter, that it felt so intimate. i didn't say anything as i couldn't relate to it, i hate it when people call me daughter and i've insisted to be called son by my parents as long as i can remember. the same week, this very nice bus driver called me son. i felt a surge of comfort, a sort of intimacy towards him. it felt like the barrier between me and the world was lifted between us. i hadnt reviewed how i liked being called son after discovering my trans status, and i had thought i liked it because of the way it is used in my language. well it turns out to be yet another trans feature
i had that same kind of realization a few years back, when some guy at a forum called me dude (gender markers weren't really visible there), and then suddenly apologized when gender markers were implemented and he realized he made a "mistake". i hated the apology, not that i could say that to someone who was just trying to be polite.