Why did Aesop used animals instead of human in its stories?

A fable is a fictitious narrative or statement.

It is also a narration intended to enforce a useful truth; especially one in which animals act and speak like humans.

Aesop is a Greek fabulist and story teller. He is credited for his collection of Aesop's Fables. Many of his tales are characterized by animals and inanimate objects that speak, solve problems, and have human characteristics. It is appealing to children when animals are the characters. Children are told fables and they are very interested once the characters are animals. I guess kids can learn from a story with animal characters which include moral lessons.