Frequent mouth ulcers in 12-year-olds may be related to poor eating habits, vitamin deficiency and other reasons. 1. bad eating habits: 12-year-old children who often eat or eat too much spicy and stimulating food at once, or usually do not like to drink water, drink too little water, can also appear mouth ulcers. 2. Lack of vitamins: 12-year-old children often mouth ulcers may also be related to the lack of vitamins in the body, if there is no timely and sufficient amount of vitamin supplementation, it is likely to lead to recurring mouth ulcers. In addition, it should be noted that the 12-year-old child if the mouth ulcers, accompanied by pain and swelling, it is recommended that timely medical treatment will be faster recovery.