2 1/2 years: Conveying whole thoughts by employing just a few words, like saying "Mommy no socks" for "Mommy isn't wearing any socks today."

3 years: Speaking in longer sentences; putting several thoughts together to tell a story; using about 300 words; following a story line and remembering ideas from it; enjoying nonsense phrases

4 years: Having extensive conversations with adults; using adjectives in detailed sentences; telling knock-knock jokes; asking questions with proper intonation

5 years: Using expressive vocabulary of 2,500 words; understanding 14,000 words; expressing complicated thoughts like fears and dreams; saying "thank you"; using words to elicit reactions from others

Reporting by Colleen Davis Gardephe

Sources: Johns Hopkins University; J. Lane Tanner, MD, FAAP; Kathy Hirsh-Pasek, PhD; John Bonvillian, PhD

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Content courtesy of American Baby.