को: SocialRel ~> Recipient

Nouns such as "children" (which seems to be a fossilized expression from back when there were several competing postpositions for social relations) will have [ss SocialRel--Recipient]. One interpretation is that the parents "receive" children, and that is why other social relations aren't included in this postposition. However, Old Hindi/Urdu seems not have had this restriction so it's iffy.

* [gex 001 "{दम्पति couple} {[pspecial "को" hi/ko SocialRel--Recipient] DAT} {कोई any} {संतान offspring} {नहीं not} {थी be-PST}।" "The couple did not have any children."]