The causes of swollen mouth in children are trauma, mouth ulcers, allergies and so on. 1. Trauma: children accidentally fall, hit by something else in the mouth, is the most common cause of mouth swelling, most of the swelling in addition to obvious pain, need to carefully check whether there is a break, if necessary, go to the hospital. 2. Mouth ulcers: If there are mouth ulcers on the upper and lower lips, the local inflammatory stimulus will also cause swelling and severe pain, and infants may experience increased drooling. 3. Allergy: If the child ate special food, contact with special items, caused by lip skin allergies, may also appear swollen mouth accompanied by itching discomfort. If you find that your child’s mouth is swollen, take him or her to the hospital to find out the cause of the swelling and then treat him or her promptly.