Cooing typically begins around 2-4 months of age, and it peaks around 6-8 months of age. Infants typically coo when they are happy, content, or engaged with their environment. Cooing can also be a way for infants to communicate their needs, such as hunger or tiredness.
There are many different theories about what causes cooing. Some researchers believe that cooing is a result of infants' vocal cords vibrating as they breathe. Others believe that cooing is a learned behavior, and that infants learn to coo by imitating the sounds that they hear from their parents and other adults.
Cooing is a normal and important part of infant development. It is a sign that an infant is developing their vocal cords and their ability to communicate. Cooing can also be a way for parents to bond with their infants and to learn about their needs.