Children have a rich capacity to develop and to acquire language or many languages simultaneously, according to esteemed linguist Noam Chomsky. This assumption is rooted in Chomsky's belief that children are born with an innate ability to comprehend language much more so than adults. As you age from childhood and into adolescence and beyond, your ability to learn additional languages depletes. Other stages of language development are also defined by Chomsky in his research.
According to Chomsky, language development is the direct result of an individual's ability to unfold a "genetically defined program" that every child is presumably born with. He believes that all children are born with the ability to discern language and understand grammar as a product of years of evolution and genetic adaptation. As such, Chomsky chose to define this innate ability as a "universal grammar," which he believes is the basis for how all humans develop a chosen language.
Chomsky believes that very early in a person's life a critical period of language development will dictate his ability to develop and comprehend language for the remainder of his life. During this period, which Chomsky believes occurs roughly around the age of 4 months, a vast level of human maturation occurs that provides the foundation for understanding language. With the appropriate external stimulation (such as a household's preferred language), people develop a type of "binocular vision" that paves the way for further development.
As a person continues to age, Chomsky believes, language development enters a stage of perfecting what has already been learnt by the individual in an effort to truly "comprehend" a language fully. In other words, Chomsky believes that to fully know a language a person must develop the ability to produce an infinite number of sentences never spoken before and to understand other sentences never heard before. This ability was defined by Chomsky as the "creative aspect" of language.
Despite Chomsky's belief that children have a higher capacity to learn a new language in comparison to that of adults, this is not to suggest that adults cannot also learn a new language if needed. Furthermore, Chomsky also suggests that a person's upbringing and social external stimuli can differ from one culture to the next and may impact the individual's overall ability to formulate a language.