Hello, I can understand your concern. Has he suffered any trauma recently in the chin area? The area you have described swells when left sided lower front teeth are infected. It can be due to trauma to the teeth or involvement of teeth by decay that oozes pus near root can causes swelling of the lower lip and area below chin. Alternatively, in case of absence of infection, he might be suffering from allergic reaction to some food or environmental substance. I would advise you to visit a dentist for diagnosis of infection in the loower front teeth. Further treatment can be advised after the confirmed diagnosis for the swelling. I hope this information helps you. Thank you for choosing HealthcareMagic. I wish your son feels better soon. Best, Dr. Viraj Shah