Is any one aware of recent practice on whether an infant in F can be taken back to someone in J or Y during the flight for part of the time? Or must he stay in F?

The closest thread I could find on point was "Visitor" - Caretaker Between Different Travel Cabins, which contained conflicting points on the same question. Perhaps the official policy is that it is barred but the practice is it's allowed (in moderation). That seems to be my sense of US carriers. But I'm not sure if things are different in recent times. I didnt bump the old thread because I thought some of the virulent postings in it were better left in the past.