Infants with six-month-old limp legs do not support the ground, generally speaking, is a normal physiological manifestation, but there may also be pathological factors such as neuromuscular system developmental delay. 1. Normal physiological performance: infant development has its own unique rules, 6 months old baby just learned to sit down, because of its legs muscle development is not perfect, so can not fully support their own bodies, is a normal physiological performance. 2. Pathological factors: 6 months of infants, legs can not support the ground, may also be the possibility of delayed development of the neuromuscular system, and the neuromuscular system caused by delayed development of many diseases, such as prematurity, ischemic hypoxic encephalopathy, intracranial tumors and so on. There may be other reasons why a baby’s legs are weak at six months, so it is recommended that you go to the hospital in time for a complete examination to determine the cause of the problem, and then give targeted treatment under the guidance of the doctor.