To name the gender of your offspring, why relate to sky terminology?
Son/Zoon/Sohn vs Sun/Zon/Sonne
Dochter/Tochter/Daughter vs Ochtend and Dageraad/Tag/Day
Compare this with: Mother earth: matter Father sky: feather
I would assume it to come from the metaphores for the parents: matter and feather.
So the family tree is based on the Ancient divinity family tree.
Earth (matter-mother) and sky feather-father produce Sun (Son) and dageraad (daybreak-daughter).
Compare nature with Greek andros (man) and neter (Ancient Egyptian god).
In my spare time I research unusual cognates based on the idea that the concrete world served as a metaphore for abstract ideas like human family relations in this case. I have to say by asking questions like this on the Linguistic Stack Exchange my reputation there was ruined by people who can not imagine such reasons for relations between words. I have hopes the philosophy community can provide insights that can help prove or disprove such relations.