What is a 3 to 4-year old vocabulary is like?

At three to four years of age, children start speaking in three- to five- word sentences and sometimes use ‘and’ to construct even longer sentences. Between two-and-a-half and four years of age they can say the consonant sounds of F and Y, and between ages two and six the sounds of T and Ng. They learn vocabulary and grammar simultaneously. Preschoolers start making new language errors of grammar and syntax, because their brains are moving from straight mimicking of words to beginning to grasp the complex rules of their mother tongue.