Amazon calculates a product’s star ratings based on a machine learned model instead of a raw data average. The model takes into account factors including the age of a rating, whether the ratings are from verified purchasers, and factors that establish reviewer trustworthiness.
My four year old daughter listens to these stories each night. She doesn't do so at my request but rather she asks for them. I'm just happy that this allows her to relax long enough so she can drift off to sleep.