Hi dear , As per your query your son has aphthous ulcer in mouth . There can be many reasons for aphthous ulcer in children like food allergies, a poor diet, a reaction to a viral infection, or an autoimmune disease may also play a role. minor injuries like chelical injuries fron some food and allergy to any dental products can produce aphthoul ulcer . Usually they go away in few days without any treatment . Do not give your child foods that can cut or scrape the inside of the mouth . Foods that are spicy, salty, or acidic (lemons and tomatoes) can irritate the gums and aggravate sores. If ondition doesn t improve in few days then again consult dentist or pediatrician for proper diagnosis and to rule out condition like herpes . He or she may prescribe a topical medicine, special mouthwash, or home remedy to help heal the sores. Hope your concern has been resolved. Get Well Soon. Best Wishes, Dr. Harry Maheshwari