Language skills blossom around age 4, and preschoolers can now pronounce most sounds of the English language. Their vocabularies expand to approximately 1,500 words, and they will gain another 1,000 before their fifth birthday. They are able to tell elaborate stories that consist of more complex sentences with up to eight words.
References:
Shelov, S. P. (Editor-in-Chief). (2004). Caring for Your Baby and Young Child: Birth to Age 5. The American Association of Pediatrics. Revised edition. New York: Bantam Books.
