Baby’s thumb is a normal physiological phenomenon, usually in 3~4 months will disappear, the latest will not be more than 6 months, if more than 6 months there is still the phenomenon of thumb buckle, it may be related to developmental delay. When a baby is born, the thumb is surrounded by the remaining 4 fingers when making a fist due to the tightness of the flexor muscles, which is manifested as an inward-facing thumb. When the child is 3 to 4 months old, as the body gradually begins to develop, muscle tone will gradually change, then the flexor muscles will gradually relax, and the phenomenon of the thumb will disappear. However, there is a certain degree of individual variability, and some children may lose it by 5 to 6 months, but not later than 6 months. If the phenomenon of thumb inward fasting still exists after 6 months, it may be related to developmental delay, which is mainly affected by the damage to the central nervous system, and some babies may also have mental retardation and motor retardation at the same time. Parents need to closely monitor their baby’s bunions. If bunions persist beyond 6 months of age, they should be examined promptly and treated according to the cause of the bunions.