I have never heard of plastic causing diarrhea, but it could be possible. The more like culprit was undercooked meat or undercooked food. Most diarrheal illnesses are caused by virus, but bacteria can also cause diarrhea. Bacteria is most commonly associated with a group of people getting sick that all ate the same food. The diarrheal generally starts about 6-24 horus after ingestion of contaminated food. If your son was recently sick, or recently used an antibiotic, then the diarrhea illness can last much longer. The diarrheal will go away on its own. In the meantime, I would recommend: -frequent handwashing -cook all food properly, avoid undercooked foods -probiotics -double fluid intake with gatorade or pedialyte. -Encourage food. -Try bananas, rice, applesauce, toast (BRAT) diet -During periods of active diarrhea, coffee, alcohol, dairy products, fruits, vegetables, red meats, and heavily seasoned foods may exacerbate symptoms. -See a doctor if it does not resolve in 5-7 days. You will need routine screen blood work and stool studies