Interesting. You're right as far as English goes. In (Mexican, at least)Spanish, however, hijo(son) and hija(daughter)are both used frequently by both sexes, both as terms of affection and as calling (negative) attention to progeny. They are also used to refer to unrelated youngsters and spouses but never to ones elders. I'll have to mull over other uses.

Variations: hijito (little son), hijita (little daughter), mijo (my son), mija (my daughter), mijito (my little son), mijita (my little daughter)

BTW, welcome aBoard, Dgeigh