My son was ill last weekend with a stomach bug, vomiting and diarrhea bouts. a week later, he has gray loose stool. would a probiotic help?

It may: Probiotic may help , and diet.

I am concerned: that the grey stools may represent lack of bile due to biliary obstruction secondary to Hepatitis A which may start as a "stomach bug" If so Probiotics will not help and the disease in kids is very mild..usually no jaundice. This is just :"a thought" but its worth mentining it to your son's Pediatric Provider .... Hope this helps and BTW HANDWASHING is important in prevention of spreading !