Hi Welcome to HCM Diarrhea once in two month may be due to other causes as well or due to intake of milk products or the lactose containing products. If the child has not consumed lactose containing product then the diarrhea may be due to food poisoning. Decreasing or removing milk products from the diet usually improves the symptoms. You can add lactase enzymes to regular milk or take these enzymes in capsule or chewable tablet form. Not having milk in the diet can lead to a shortage of calcium, vitamin D, riboflavin, and protein. These should be supplemented. If the loose motion is severe, dehydration can occur it should be addressed. Hope i have provided the information you needed. wish your son good health. Take care.