They can be good pets for kids because they don't bite or scratch like other rodents. As their teeth continue to grow with age, they have to be provided with some twigs or chew toys to ensure that they don't become too large.
They don't require vaccination, but they can suffer from ailments such as respiratory infections and diarrhea. Mange is observed to be a common cause for hair fall and excessive scratching in Guinea pigs. They also suffer from lice and fungal infections.
Cavies are easy to domesticate because they have a good memory. Their sharp senses of smell, hearing, and touch, compensate for their poor eyesight. When they are attacked by a predator, they tend to run haphazardly; it's their defense mechanism to confuse the predator.
Guinea pigs were domesticated for meat by ancient tribes. Come today, they have become an integral part of the diet in many parts of South America. People of Peru alone consume around 65 million guinea pigs every year.
Pro Tip: When selecting one as a pet, choose an alert and active individual, as the ones which are very quiet and calm are likely to be ill. A healthy pet guinea pig can give you company for 7 - 8 years.