The following baby mobs that don't make idle sounds;
-Baby Pigs
-Baby Sheep
-Baby Chickens
-Baby Cows
-Baby Mooshrooms
-Baby Ocelots
-Baby Wolves
-Baby Squids
-Baby Mules
-Baby Donkeys
-Baby Horses (all)
-Baby Villagers
-Baby Zombies
-Baby Zombie Villagers
-Baby Zombie Pigmen
-Baby Husks
They do not make any idle sounds, whether they spawn naturally, or spawned in creative.
Apparently this affects baby hostile mobs as well.