1. American Speech Language and Hearing Association. (2009). How does your child hear and talk? Retrieved January 9, 2009, from
http://www.asha.org/public/speech/development/chart.htm
2. National Library of Medicine. (2007). Developmental milestones. Retrieved January 9, 2009, from
http://www.nlm.nih.gov/medlineplus/ency/article/002348.htm
3. Owens, R. E. (2001). Language development: An introduction (5th ed.). Needham Heights, MA: Allyn and Bacon.