Final answer:
It takes immigrant children generally 3-5 years to become proficient in English, factoring in the natural language acquisition abilities of young children and the level of language immersion.
Step-by-step explanation:
Researchers have found that it generally takes immigrant children 3-5 years to become proficient in speaking English. This timeframe can vary based upon individual circumstances, such as the age at which the child begins learning the language and the level of immersion in an English-speaking environment. The human brain is remarkably adept at acquiring language during early childhood, and with adequate exposure, children can rapidly absorb the rules and vocabulary of a new language. This proficiency, of course, includes various stages of language development, starting from understanding simple words to the ability to use language to express complex ideas and engage in abstract thinking.