Children's oral ulcers are often caused by a deficiency of trace elements, a deficiency of B vitamins, a decrease in immune function during illness, or insufficient intake of vegetables and fruits, which often leads to oral ulcers. Therefore, the following methods can be adopted:

1. You can grind vitamin B2 into powder and apply it externally to the mouth;

2. You can use Kangfuxin solution for topical use 3-5 times daily, where topical means applying drops to the ulcer;

3. You can spray watermelon frost on the affected area 3-5 times daily;

4. You can use oral ulcer patches.

Therefore, it is important to maintain a balanced and reasonable diet in daily life, and to pay attention to the regulation of children's immune function.

(The use of medication should be under the guidance of a doctor.)