Children can’t close their mouths when they sleep, which may be caused by rhinitis, stomatitis and tonsillitis. 1. Rhinitis: Nasal congestion, itchy nose and sneezing will occur. If children suffer from rhinitis, when the nose is blocked, it is not easy to breathe, they may use their mouths instead of breathing, which induces them to sleep with their mouths closed. 2. Stomatitis: the patient’s oral mucosa will appear congestion, edema and ulcers and other symptoms, mostly accompanied by pain. If children have pain when closing their mouths, it may trigger the phenomenon of not closing their mouths in sleep. 3. Tonsillitis: Fever, throat discomfort, pain, and difficulty breathing may occur. If a child suffers from this disease and has difficulty breathing through the nose, he or she may open the mouth to breathe, which may cause the mouth to not close in the sleep. There may be other reasons why children can’t close their mouths when they sleep, so it is recommended that they go to the hospital in time for a complete examination to determine the cause of the disease and then give targeted treatment or therapy.