The deeper question here is why we feel the need to imitate animal sounds when we have words to describe the animals. Before we had language, “Moo,” was a good way to alert neighbors to a food source. Now, when we can say, “There’s a herd of cows grazing just over the grassy knoll,” “Moo” seems terribly obsolete. Of course, there are still a few functional reasons to make animal sounds: birders do it to attract different species to look at, pet owners do it out of some empathic desire to connect with their pets. But why do children do it?
Try it out yourself.