A: Dear ppk2000:
The likelihood is that your son is perfectly fine, as some babies do not talk or walk at 16 months and sleeping through the night is not achieved by some babies for a protracted time. It is good that you think he understands everything (and you are probably right!), since most babies understand a great deal of language before they actually say anything themselves. Boys are often late talkers and large, heavy babies can be slow to get moving in comparison to wiry little ones.
However, since early treatment can be very important for the unusual case where there is some sort of problem, it would be worthwhile visiting your family doctor or pediatrician just to make sure. It is not possible for me to give you complete reassurance without meeting your son in person--so to be on the safe side, I would suggest you arrange for a physician to see your son face-to-face and address your concerns.
Elizabeth Berger MD
Child Psychiatrist and author of "Raising Kids with Character"