In second language acquisition, The Critical Period Hypothesis (CPH) holds that there is a critical time period for a person to learn a new language with native proficiency. This time usually begins around the age of two and ends just before puberty. According to the hypothesis, learning a new language after this critical period will be more difficult and unsuccessful. The crucial phase is the stage of a person's development when their nervous system is primed and sensitive to environmental stimuli, according to developmental psychology. If a person does not receive the appropriate environmental stimuli during this time, their capacity to learn new skills will deteriorate, compromising a variety of adult social functions. If a child does not learn a language during this vital era, they are unlikely to achieve native fluency in their first language. Because of the adaptability of the brain, a person is poised to learn new abilities throughout the critical period. Synapses, or brain connections, are extremely receptive to information. Some researchers refer to the'sensitive period' or weak critical period' as a synonym for the critical period. The sensitive phase is comparable to thecritical period in that it is characterized by a high level of neuroplasticity and rapid formation of new synapses in the brain. The key distinction is that the sensitive phase is thought to endure longer than puberty, but there are no hard bounds.

The development of verbal fluency is associated with the maturation of executive function skills, such as the ability to inhibit irrelevant information, shift between tasks, and hold information in working memory. Some evidence suggests that multilinguistic upbringing may underpin disadvantages in verbal fluency and lexical retrieval, but can also afford executive function advantages beyond the language system including possible beneficial effects in older age. This study examined the relationship between verbal fluency and executive function in 324 individuals across the lifespan by assessing the developmental trajectories of English monolingual and multilingual children aged 7-15 years (<i>N</i> = 154) and adults from 18 to 80 years old (<i>N</i> = 170). The childhood data indicated patterns of improvement in verbal fluency and executive function skills as a function of age. Multilingual and monolingual children had comparable developmental trajectories in all linguistic and non-linguistic measures used in the study with the exception of planning, for which monolingual children showed a steeper improvement over the studied age range relative to multilingual children. For adults, monolinguals and multilingual participants had comparable performance on all measures with the exception of nonverbal inhibitory control and response times on the Tower of London task: monolinguals showed a steeper decline associated with age. Exploratory factor analysis indicated that verbal fluency was associated with working memory and fluid intelligence in monolingual participants but not in multilinguals. These findings raise the possibility that early acquisition of an additional language may impact on the development of the functional architecture serving high-level human cognition.

In second language acquisition, The Critical Period Hypothesis (CPH) holds that there is a critical time period for a person to learn a new language with native proficiency.  This time usually begins around the age of two and ends just before puberty. According to the hypothesis, learning a new language after this critical period will be more difficult and unsuccessful. The crucial phase is the stage of a person's development when their nervous system is primed and sensitive to environmental stimuli, according to developmental psychology. If a person does not receive the appropriate environmental stimuli during this time, their capacity to learn new skills will deteriorate, compromising a variety of adult social functions. If a child does not learn a language during this vital era, they are unlikely to achieve native fluency in their first language. Because of the adaptability of the brain, a person is poised to learn new abilities throughout the critical period. Synapses, or brain connections, are extremely receptive to information. Some researchers refer to the'sensitive period' or 'weak critical period' as a synonym for the critical period. The sensitive phase is comparable to the critical period in that it is characterized by a high level of neuroplasticity and rapid formation of new synapses in the brain. The key distinction is that the sensitive phase is thought to endure longer than puberty, but there are no hard bounds. Keywords: Critical period hypothesis, Second Language acquisition

The Critical Period Hypothesis is still controversial recently, so it cannot be said to be absolutely confirmed to be false. It is more important to realize the significance of application. Although the exact properties of this phenomenon remain unclear and the literature is divided, more and more Chinese mothers choose to teach English or other languages as a second language to their children from a very early age (0-3 years old). This paper discusses whether these attempts can help children achieve the future goals set by their parents through literature review. The results attempt to support the existence of the Critical Period Hypothesis, because from the end of adolescence, the ability to learn grammar declines sharply, and the ability to reach native-like proficiency depends largely on the age at which learning begins.