What causes mouth ulcers in a three-and-a-half-year-old child?

Possible causes of oral ulcers in a three-and-a-half-year-old child may include the following: 1. **Improper diet**: If the child frequently consumes spicy, irritating, or excessively hot foods, it may damage the oral mucosa and subsequently lead to oral ulcers. 2. **Vitamin deficiency**: Particularly a deficiency in B-complex vitamins, which may reduce the resistance of the oral mucosa and trigger oral ulcers. 3. **Viral infection**: Such as herpes simplex virus or Coxsackievirus. These viral infections may cause blisters on the oral mucosa, which then rupture and form ulcers. 4. **Trauma**: During play or eating, the child may accidentally bite the oral mucosa, resulting in traumatic ulcers. When parents notice oral ulcers in their child, they should carefully observe and try to identify potential causes. Medical attention should be sought when necessary.