I suspect that it never occurred to Hef that Kelsey might bring a baby with him.
Since the child is so young, I don't see a problem with cleaning up language, and so forth. I also bet that the Playboy Mansion parties are much duller than the venue would suggest, and have heavy security. Presumably, guests who act in a bizarre or belligerent fashion are removed.
What does concern me is whether the music or the other party activities were too noisy for tender baby ears. I would guess that there is a decibel level above which an infant's hearing could be damaged.
IMHO Grammar wanted to *show off* and be "cool." There is a lot of publicity these days about Hollywood babies. pregnancies, breastfeeding etc. I think that Kelsey just wanted to emphasize that he was/is young enough still to father a child.
For some reason the old expression about mutton being done up like lamb keeps coming to mind.
I do think that it was a bit OTT to take the infant to the party, but I doubt he inconvenienced anyone very much.
Grammar's actually been much ruder, though, in some of the statements that he's made about his X. IRL he must be quite a character.