I have noticed that this topic is coming up frequently on our board so I thought I would share some information that I uncovered while doing my Child Development classes. I also found this information very helpful when deciding to get D evaluated. The earlier intervention takes place the better the outcome. I hope this information is helpful
Article about language developmenthttp://www.asha.org/public/speech/disorders/lateblooming.htm
CDC Milestone charthttp://www.cdc.gov/ncbddd/actearly/milestones/milestones-18mo.html
Also, every state has an Early Childhood Intervention program. You can have your child's language evaluated by a speech therapist for no cost.