The causes of mouth ulcers in children may be genetic, immunologic, psychiatric, dietary, and traumatic. 1. Heredity: Canker sores have a certain family aggregation phenomenon, and there is a certain relationship with heredity, if the parents have canker sores, the child has a greater chance of suffering from canker sores. 2. Immune factors: children with low immunity are susceptible to invasion by a variety of pathogens, so they are prone to mouth ulcers. 3. Mental factors: if the child’s mental stress is relatively large, often have anxiety, tension and other negative emotions, also easy to trigger mouth ulcers. 4. Dietary factors: if the child partial food is prone to vitamin deficiency, easy to cause mouth ulcers, if the lack of zinc will affect the cell division and regeneration, also prone to mouth ulcers. 5. Trauma factors: if children often eat some hard, sharp food or need to wear orthodontic braces, etc., may cause trauma to the oral mucosa causing ulcers. Children’s mouth ulcers may also have other reasons, it is recommended to go to the hospital in a timely manner, improve the examination to clarify the cause of the disease, give targeted treatment or treatment.