I took the Silithid Hatchling pic, found them in both of the Silithid areas in Tanaris (Noxious Lair, Gaping Chasm.) I can't remember what the weather was like, but I'm guessing it and the Guardling spawn during a Sandstorm.
Duerma wrote: I have not found the flayer hatchling in Hellfire Peninsula, and I flew all over the zone. I have not found the baby ape in the Cape of Stranglethorn (should spend more time there though).
Apparently the Flayers can be found on Razorthorn Rise, which is technically in Terokkar. The Apes spawn on Jaguero Isle when it rains.