Many researchers have found that when children learn a language before adolescence they are more likely to have native-like pronunciation. There are many factors that play a role in this, including the speed and frequency with which caretakers speak to children. For example, consider how adults often change their tone of voice to make it more “child-friendly.” The way in which young children learn is a way that nurtures accurate and detailed language acquisition.
Researchers disagree on the precise reasons why children's brains may be more susceptible to language acquisition, and some say it has nothing to do with a critical developmental period at all. It is clear though that the environment in which children learn aids in this process. It is common for all caretakers in a young child’s life to support the child in learning precise sounds and syllables in a native language. This focus on accurate language acquisition tends to fade in adolescence when education becomes more specialized.
The correlation between age and proficiency of language acquisition also plays a role in children becoming multilingual. Research has also shown that children who grow up speaking more than one language are more likely to have native pronunciation in both languages than individuals who learn a second language in adolescence or later.