Final answer:
By 5 years old, most children should have acquired adequate speech and language ability, with a substantial vocabulary and the capacity to form complex sentences and engage in conversations.
Step-by-step explanation:
Most children have acquired adequate speech and language ability by 5 years old. By this age, children have developed a vocabulary of at least 1,500 words and produce sentences of at least five to seven words. They can carry on conversations, recognize letters and words, and possess the ability to define words by their function. Additionally, their cognitive and psychosocial development enables them to sort objects, count past 20, and understand calendars and clocks. The rapid language learning phase occurs between nine months and three years, and while a vocabulary spurt might be observed around 2 to 3 years old, with a significant increase in vocabulary, it is at five years old that children demonstrate more consistent and complex language skills, including the use of slang and understanding of jokes.
Three-year-olds can speak in short simple sentences and ask questions, showing an impressive leap from the one- and two-syllable words they typically use as one-year-olds. By the time they are seven, children speak fluently and continue to refine their language skills as they grow. This developmental trajectory sees kids still expanding their vocabulary and improving in language composition well into their middle childhood years, roughly between six to ten years old.