> it is only applied to women as an endearment

Could it be that a lot of such familial and familiar terms of endearment have a p/b consonant in or at the front of them? ..bub, bud, pal, pop, pard, buddy, bro, pa... So is bub part of a word cluster? Isn't the b/p sound one of the first the be pronounced by children? Maybe there's some relevance.