The causes of drooling in children’s sleep include small oral cavity capacity, upper respiratory tract infections, oral diseases, and so on. 1. Small oral cavity capacity: the oral cavity capacity of small children is relatively small. When they sleep at night, the secretion of saliva is more, and they can’t swallow it into the gastrointestinal tract in time, so they may drool. 2. Upper respiratory tract infection: small children with upper respiratory tract infection and nasal congestion, sleep usually need to open the mouth to breathe, can not swallow saliva in time, thus the phenomenon of drooling. You need to actively treat the disease to relieve the symptoms of nasal congestion. 3. Oral disease: oral herpes, gingivitis, periodontitis and other oral diseases, on the one hand, the oral secretions increase, on the other hand, oral pain will affect the normal function of swallowing, small children may appear to sleep drooling. There may be other clinical reasons for drooling in sleep. Parents are advised to take their children to the hospital to determine the specific cause of drooling.