Hey, this may seem like a big oversight, but I just realized those quotes above were from Cicero. I had assumed they were from Epicurus.
So maybe I've conceded too much.
I don't see any references to babies or animals in either the PD or the Letter to Menoeceus. Of course that doesn't prove Epicurus didn't use the cradle argument. But the case remains open!
Doesn't change anything in my positions, but it sure was disappointing to read a full-throated endorsement of the cradle argument and think it was coming from Epicurus!
Furthermore, FWIW, the second paragraph sounds like some inter-Epicurean debates around this. In the time of Cicero(?) so I'll take that with a big grain of salt...but there may be more support for my anti-cradle argument than I first thought.