3-year-old children crying at night may be caused by physiological factors, vitamin D deficiency rickets, eczema, gastrointestinal lesions and other factors. 1. Physiological factors: such as nightmares, environmental factors, etc., may cause the child to cry at night, should be timely to calm the child, and improve the environment, usually can be relieved. 2. Vitamin D deficiency rickets: 3-year-old children partiality and picky eating, leading to a lack of vitamin D in the body, easily caused by calcium deficiency, will be crying at night, accompanied by restless sleep, can affect the normal development of the body in serious cases. 3. Eczema: may be related to environmental factors, immune factors, can lead to the appearance of red pimples on the body, accompanied by intense itching, will cause the child to sleep at night crying. 4. gastrointestinal lesions: for example, acute gastroenteritis, dyspepsia, intestinal obstruction, etc., may cause abdominal distension, abdominal pain and other symptoms, can make the child cry at night. 3-year-old children crying at night may also have other reasons, it is recommended to go to the hospital in time, improve the examination to clarify the cause of the disease, under the guidance of the doctor to give targeted treatment or treatment.