There's little evidence that humans actually believed that babies were delivered by storks. But what people DID believe about human procreation is a very interesting story.
For example: the prevailing theory was that little tiny people, fully formed, resided in the sperm. Women were only necessary as the garden in which the seed grew.
This and other bad guesses are explored in Edward Dolnick's book The Seeds of Life: From Aristotle to da Vinci, from Sharks' Teeth to Frogs' Pants, the Long and Strange Quest to Discover Where Babies Come From.
The author visited in 2017 to peruse the stories; we rejoin the interview here.