A lot of kids on the spectrum also have muscle tone issues which can contribute to constipation. If your son had physical developmental delays, that can be one sign of such a problem, which a neurologist is best at detecting. My daughter and occasionally my son both take a small amount of GlycoLax in some juice when this becomes an issue. I am not sure as to whether it is GFCF, but I suspect so, as many children on special diets use it. I was told to keep my children on GlycoLax (also called Miralax) until they were potty-trained, as retention can lead to a real aversion to using the potty. Good luck.

Cynthia