V.J.
I wonder if they could have an intestinal parasite like crytospridium or giardia. I just read a news article recently about several public pools in Phoenix closing because of cryptosporidium contamination that was causing people to become ill. http://www.azcentral.com/arizonarepublic/news/articles/20...
Here is some more info I found:
"Cryptosporidium is associated with water-borne outbreaks. The victim might experience diarrhea and abdominal pain lasting for about ten days.
Giardia is the most prevalent intestinal parasite in humans and found in drinking water. Symptoms are mild to moderate abdominal cramps, intestinal gas, light colored stools, bad absorption, weakness, chills, stomach bloating and diarrhea."
Maybe you could get a stool sample tested at the pediatrician to rule it out. It's a little disappointing that their doctor kind of blew it off like that. I know how that can be. Best of luck...I hope they get well soon. :)