https://www.reddit.com/r/AskAnthropology/comments/38ikwr/did_manchu_women_really_fellate_their_sons/

I read some time ago that the Manchu people believed kissing on the face to be a purely adult and sexual act. As such they considered kissing their children's faces taboo, and instead showed affection by fondling their genitals (for girls) or fellating them (for boys). The rationale for this was that genitals were not sexual until adulthood.