9-month-old infants crying in the middle of the night may be related to physiological factors, or may be caused by vitamin D deficiency rickets, indigestion, acute gastroenteritis and other causes. 1. Physiological factors: for example, the sleeping environment in which the 9-month-old baby is sleeping is too cold or too hot, or the stomach is hungry in the middle of the night, urination, etc., may cause the 9-month-old baby to cry in the middle of the night. 2. Vitamin D deficiency rickets: nine-month-old infants with rickets will lead to increased neural excitability, which can easily lead to dreamy sleep and easy to wake up, and may show the middle of the night crying, which can also be accompanied by difficulty in falling asleep, occipital baldness and other manifestations. 3. Indigestion: If parents add complementary foods to their 9-month-old babies, due to improper feeding, it may lead to indigestion, causing abdominal distension and abdominal pain, which may cause crying in the middle of the night. 4. Acute gastroenteritis: 9-month-old infants with improper diet, such as overeating, excessive consumption of cold or unclean food, is likely to induce acute gastroenteritis, may appear in the middle of the night crying phenomenon, may also be accompanied by vomiting, diarrhea and other manifestations. Nine-month-old babies crying in the middle of the night, may also be caused by other reasons, to rule out physiological factors, it is recommended to seek medical attention as soon as possible, to clarify the cause, to give targeted treatment.