Updated: Sep 8, 2019
When you say baby/young animals in Japanese, it is much simpler than in English! This is because English has individual names for baby/young animals distinguishing from adult animals (male and female animals). In Japanese, however, there aren't unique names for baby animals - you can just add the word “ko” (child/kid/infant) before the animal name. You also don’t need to consider their gender (male/female)!
Let’s check some examples.
If you want to say the animal gender, for example “a male puppy”, you can say “osu no koinu”. The “osu” means “male”, while the “mesu” means “female” for animals. However, when it comes to humans, you can’t use “osu” and “mesu”! Also, some people treat their pets as their family members, more than just pets, so they don’t want to use “osu” or “mesu”.