A baby mouse is called a mouse pup or a pinky. The term pup is more commonly used. The term pinky is typically used to refer to baby mice that are sold as feed for pet reptiles.
The term pinky is only used for baby mice that are fewer than 6 days old and still hairless and pink in color. The term pup is used for the entire growth period before weaning, which takes place at around 3 weeks old. Female adult mice are called does, and male adult mice are called bucks. Mice stop growing and reach sexual maturity at approximately 6 weeks old.