To help your son with constipation, you can try giving him more fruits, vegetables, legumes, and whole grains. It's also important to make sure he stays hydrated by drinking enough water. Being active and moving his legs regularly can also help with bowel movements. If these changes don't improve his constipation, it may be necessary to consult a doctor for further advice. Avoid using over-the-counter products like laxatives or fiber supplements without a doctor's recommendation, especially for a young child.