A two-year-old baby crying every night may be caused by unsuitable temperature and humidity or diseases such as vitamin D deficiency and roundworm disease. 1. Unsuitable temperature and humidity: the temperature and humidity change greatly at night, if you don’t give the baby good warm measures, the baby feels cold or hot when sleeping may wake up, thus appearing to cry every night. 2. Vitamin D deficiency: Vitamin D deficiency is a disease caused by vitamin D deficiency, mostly associated with insufficient sunlight, improper diet and other factors, if the baby suffers from vitamin D deficiency, there will be increased neurological excitability, resulting in waking up at night, restlessness and other symptoms, which will also lead to the baby crying every night. 3. Ascariasis: Ascariasis is a disease caused by roundworm parasites in the small intestine or other organs of the human body, which is prevalent in children. If suffering from intestinal ascariasis, the child will have neuropsychiatric symptoms, such as convulsions, night terrors, and teeth grinding. As roundworms move around a lot at night, they can cause babies to experience abdominal pain and other discomforts at night, which can lead to the situation of two-year-old babies crying every night. There are more causes for two-year-old babies to cry every night, so parents are advised to take their children to the doctor for examination and clear diagnosis.