Quote:i want to say something like "The Walrus's baby is very playful"
Note that walrus is not ordinarily a proper noun so you would not normally start the word with a capital W, unless you wished to pretend (like in children's books etc) that the parents were a married couple of humanised animals. E.g. Mr and Mrs Dog and their son Buster Dog. Also, animals are not normally said to have 'babies' unless they are humanised (anthropomorphised) in this way, or sometimes when talking to very young children. A young walrus is called a 'calf'.
If you are so pretending, then the married couple would be called the Walruses and their young 'baby' would be the Walrus baby, as with humans you would have the Jones baby, the Smith baby etc.
Perhaps you could clarify your intention?