Guinea pigs are not pigs. They are rodents belonging to the Caviidae family. Guinea pigs are also called Cavies (singular is Cavy). Guinea Pigs make fun family pets but make sure children handle them gently. Guinea pigs should be kept in pairs. Guinea pigs live longer than many other small pets, 5 to 7 years or longer. The average adult guinea pig will weigh about 2.5 lbs and they can grow to be 10 to 14 inches in size.