In English language, there are special vocabulary items for younger animals. It is nothing but to differentiate the younger ones from the older ones. Here is a short lesson on the vocabulary terms to denote the younger ones of various animals.
Bunny: A young rabbit. Also Kitten.
Calf: A young cow or bull. Also, the young of some other large mammals like elephant
Colt: The young of a horse
Cub: The young of a fox, bear, lion, wolf or other carnivorous mammal.
Cygnet: A young swan.
Duckling: A young duck.
Eaglet: A young eagle.
Fawn: A young deer in its first year.
Foal: A young horse or related animal.
Gosling: A young goose.
Joey: A young Kangaroo.
Kid: A child or young person, a young goat.
Kit: A young Fox.
Kitten: A young cat, rabbit and beaver.
Lamb: A young sheep.
Leveret: A young hare in its first year.
Puppy: A young dog
Whelp: A Young Lion.