Mouth ulcers in children can make eating, drinking, brushing, and talking uncomfortable. Most simple canker sores heal within one to two weeks, but the cause and accompanying symptoms matter. This guide explains five possible causes, including minor injuries, canker sores, viral infections, nutritional problems, and reactions linked to health conditions or medicines. Parents will learn how to distinguish common mouth sores, offer soothing fluids and gentle foods, and manage discomfort safely according to age. It also covers dehydration concerns, recurring ulcers, contagious conditions, and warning signs, such as breathing trouble or an inability to swallow saliva, that require urgent medical attention.