Level 1: What are oral ulcers in children? Oral ulcers are a common oral disease and one of the common oral problems in children. It usually appears as small, red, round or oval-shaped sores in the mouth with a white or yellow border around them. Mouth ulcers in children may cause mild discomfort and pain but usually do not lead to serious health problems. Level 2: What are the causes of oral ulcers in children? The causes of oral ulcers in children may be related to the following factors: 1. Sucking thumbs or other objects for a long time 2. Intraoral trauma or injury 3. Low immune function 4. Partial eclipse or malnutrition 5. Stress and anxiety