The harm of children sleeping with their mouths open mainly affects the face, respiratory tract infections and so on. 1. Impact on the face: children sleeping with their mouths open may be due to respiratory resistance caused by, such as adenoids and other easy to sleep with their mouths open, if long-term sleeping with their mouths open will cause small children to produce adenoids face, lip hypertrophy, teeth are not aligned and other impact on the face. 2. Respiratory infections: sleeping with the mouth open air directly into the body, not filtered through the nose hairs, easy to cause respiratory infections. If the child always sleeps with the mouth open, it is recommended to give the child timely adjustment, you can take the child to the hospital for a check-up to clarify the cause, by the guidance of a specialist doctor treatment.