The following red flags may indicate a child is at risk for atypical development, and is in need of an immediate evaluation.

In clinical terms, there are a few “absolute indicators,” often referred to as “red flags,” that indicate that a child should be evaluated. For a parent, these are the “red flags” that your child should be screened to ensure that he/she is on the right developmental path.
Social/Communication Red Flags
If your baby shows any of these signs, please ask your pediatrician or family practitioner for an immediate evaluation:

No big smiles or other warm, joyful expressions by six months or thereafter
No back-and-forth sharing of sounds, smiles, or other facial expressions by nine months or thereafter
No babbling by 12 months
No back-and-forth gestures, such as pointing, showing, reaching, or waving by 12 months
No words by 16 months
No two-word meaningful phrases (without imitating or repeating) by 24 months

Any loss of speech or babbling or social skills at any age “Most mommies and daddies tell me “I thought there was a problem at 14 or 15 months...and they told me let’s wait and see because sometimes some kids grow out of it.’ Well, that’s not a good answer. We’ve got to make the distinction between less important problems, where we can wait and see from core problems, which involve a lack of reciprocity and a lack of getting to know your world. For these core problems, we have to act on it yesterday. We can’t wait nine months, we can’t wait two months.” (Stanley I. Greenspan, M.D., Child Psychiatrist)

Red Flags were compiled from the following sources: Greenspan, S.I. (1999) Building Healthy Minds, Perseus Books; Filipek, P.A. et al.