Every single baby in the game, including nautiluses
Baby animals in a cherry grove
Baby pig in a village
A swarm of baby animals
Some extra baby chickens
Baby chickens next to their parent
Group of baby turtles in the beach
Baby dolphin and its parent jumping over the sunset
Baby squids and baby glow squids
Just in case using the pictures directly from the wiki is suspicious, here's some baby chickens in the overworld I just took a pic of. The ratio of babies spawning is quite low in vanilla, so it takes quite a while, and the wiki pictures are better.
Another screenshot of a naturally spawning white rabbits, adult and baby, in the snow
