Some stories simply have to be told with animal characters. Why? Because the plot involves actions that are deemed too silly or too dangerous for a "real" child. For instance, you can't have a human preschooler cross a busy city street without an adult, but, you can have a little talking cat do it. Or, you wouldn't have a human child mistaking a beach ball for a seagull's egg, but you can have a silly monkey do so.
Think about the Frank Asch books with Bear. The endearing little character hears the moon talk to him in Happy Birthday, Moon, he plays hide-and-seek with the moon and worries when it doesn't come out from behind a cloud in Moongame, Bear makes popcorn ON A STOVE in Popcorn, and he takes a rocket ship to the moon so that he can taste it in Mooncake. Try any of those story lines with a human character and you'll be thrown right out on your ear!