At what stage of development do children begin to use more complex sentences?

Children typically begin to use more complex sentences around the ages of 3 to 4 years. During this developmental stage, they start to combine words to form multi-word sentences and incorporate basic grammatical structures. This is a crucial period for language acquisition, as children expand their vocabulary and improve their ability to express ideas, feelings, and experiences more clearly.

At 3 to 4 years of age, a child may begin using simple sentences and start to include conjunctions like "and" or "but," which marks a shift from single-word or two-word phrases to more elaborate expressions. They also begin asking questions and using words like "why" or "how," reflecting their growing cognitive abilities and understanding of the world around them. This development sets the foundation for future language skills and more nuanced communication.