A rare but serious cause of green stool in kids and adults is poisoning by chemicals such as the pesticide paraquat. Green poop can continue throughout life from foods containing chlorophyll. Bacteria like Salmonella, the water parasite giardia, and norovirus are all potential causes. When green stool appears, it is important to pay attention to other symptoms that might be present to determine if medical care is necessary. Vitamins and Medication.