The plural forms of those nouns are:
You will notice that the nouns ending in 'y' preceded by a consonant change the 'y' to 'i', before adding 'es'.
The nouns that end in 'y' preceded by a vowel, simply add an 's'.
a baby monkey
a baby monkey is known as an infant
Baby Monkey was created in 2002.
They are called infants
A baby monkey is referred to as an infant.
a baby monkey.
There is no special name for a baby monkey the can just be called infants, or children
The mother of a baby spider monkey takes care of it.
A baby elephant is a calf. A baby kangaroo is a joey. A baby monkey has no special name - just baby monkey or infant.
Infants
A baby sea-monkey is called a nauplius. It is the larval stage of a sea-monkey before it develops into an adult.
The "Puppy Monkey Baby" a CGI character created by Mountain Dew for a TV commercial.