If you've just begun teaching your child great oral care habits, spotting a mouth sore can be concerning. Don't worry; it's not a reflection on how well they're brushing or flossing. Just like adults, toddlers are susceptible to mouth sores too. Mouth ulcers in kids often present in several different ways, according to Seattle Children’s Hospital. While your dentist or your primary care physician should diagnose the sore, it’s helpful to learn the signs, symptoms, and causes so you can better prevent and quickly treat mouth sores in children.