When a child laughs, his mouth is crooked mainly due to bad habits leading to a crooked smile, but also may be caused by facial neuritis and other diseases. 1. Bad habits: If children often like to smile crookedly, there will be a smile of mouth asymmetry, is a physiological phenomenon. 2. Facial neuritis: Facial neuritis is facial muscle paralysis caused by damage to the facial nerve, the patient will appear unilateral facial paralysis, the sick side of the mouth crooked, speech leakage and other symptoms, the cause of the disease and infection, inflammation, immunity, tumor and other factors. If a child suffers from facial neuritis, his mouth will be crooked when he smiles. There may also be other reasons why a child’s mouth is crooked when he smiles, so it is recommended that he go to the hospital in time, complete the examination to clarify the cause of the disease, and then give targeted treatment or therapy under the guidance of the doctor.