FAS is known to cause developmental delays, and one with feeding is something you should take seriously. I would suggest two things, first, that you contact a speech and lagnague pathologist who deals with feeding issues and understands FAS, and second, that you call your nearest childrens hospital and contact a Develompental Pediatrician and make an appointment. Because he has FAS, you should be proavtive and be on top of the delays to get the earliest possible intervention for each one.
Feeding, chewing, and swallowing food are essential to growth, but the act of moving the food from the front of the mouth to the back of the mouth and chewing develop the muscles that are necessary fro clear speech.
It is much more important for your son than for most to start seeing professionals ASAP, and do not delay when ever you ask yourself if something is typical. You should expect delays and be in constant care with a developmentalist.
M.