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 and six year old read these books together. They really loved them! They laughed several times and enjoyed the overall story. It only took them a short time to read them, which was the only negative, but I'm still glad we got them.