Children with thumb inversion may have immature muscle development, brain injury syndrome, and so on. 1. Immature muscle development: usually the muscles responsible for stretching the thumb outward may not be mature, so the thumb may appear to be inwardly fastened, which is usually a normal physiological manifestation, and often occurs in one or two-month-old babies. 2. Brain injury syndrome: If a child suffers from hypoxic-ischemic encephalopathy, intracranial hemorrhage, etc., it may lead to brain injury syndrome, resulting in central nervous system dysfunction in children, such as thumbs inward. There may be other reasons for children’s thumbs to buckle, it is recommended that patients actively seek medical treatment, improve the examination to clarify the cause of the disease, and standardized treatment.