0-6 months: Cooing, gurgling, and experimenting with sounds. 6-12 months: Babbling and starting to form simple words. 12-18 months: Using single words and understanding basic commands. 18-24 months: Combining two words to form simple sentences. 2-3 years: Vocabulary rapidly increases, and children start forming more complex sentences. 3-4 years: Speech becomes more clear, and they start using grammar rules. 4-5 years: Speech is mostly understandable, and they can tell stories and use future tense.