A 3 year old sleeping with an inward thumb is usually not normal. Thumbs inwardly clasping often occurs because the fingers are dominated by flexor tone, resulting in the appearance of an inwardly clasping thumb. Generally speaking, this situation will appear in the birth of three months within the newborn, as the baby’s age increases, the baby’s fingers gradually to the extensor muscle dominance, the phenomenon of thumb deduction will gradually reduce and disappear. So the phenomenon of 3-year-old babies sleeping with their thumbs still appearing is generally speaking abnormal. Common causes include hypoxic-ischemic encephalopathy and other early manifestations of brain injury syndromes. Parents are advised to take their children to the hospital for examination and targeted treatment after clarifying the cause.