It is normal for a 7-month-old baby not to be able to sit as long as there are no other abnormalities. In the process of pediatric development, most infants and young children in the development of 7 months may be able to sit, but the sitting time will not be too long; but due to certain differences in the speed of pediatric development, some infants and young children are slower to develop, and may not be able to sit at 7 months, as long as there are no other abnormalities, it is a normal phenomenon, do not need to worry too much. Infants and young children will not sit for a long time, and there is a thin body, other developmental abnormalities, should be alert to malnutrition, calcium deficiency, delayed motor development and other factors, it is recommended to consult a doctor for examination, to clarify the specific causes, and timely treatment, to avoid the physical development of infants and young children caused by adverse effects.