Talk to your child's dentist about how to treat mouth ulcers. The dentist may recommend medicines that you rub on the ulcers to relieve pain. If a virus is causing the sores, antiviral medicines can help.
Try to keep your child's mouth clean by brushing, flossing and rinsing with salt water. Don't give your child hot and spicy foods and drinks, since they can make a mouth ulcer even more painful.