Canker Sores (for Kids) - Nemours KidsHealth
Canker sores are round and usually about the size of a kernel of corn (¼ inch, or 6 millimeters), but they can be bigger. If you look in the mirror at your canker sore, it will be white or yellow with a red border. Canker sores hurt, especially if you eat something hard, crunchy, salty, or acidic (like orange juice).
