At age 3, most children have active vocabularies of 300 or more words, talk in sentences of five or six words, and imitate most adult speech sounds. Children this age tend to chatter constantly, practicing and perfecting the use of their new skills.
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.