A six-year-old child crying at night may be caused by abdominal discomfort, calcium deficiency, fever and other reasons. 1. abdominal discomfort: abdominal discomfort may be caused by overeating, colic, intestinal cramps and other reasons, which may cause the six-year-old child crying at night. 2. Calcium deficiency: If a child has a calcium deficiency, it can affect physical development. There may be symptoms such as growing pains, leg cramps, fatigue, partiality, and poor dental development. It may even cause disturbed sleep, resulting in crying at night. 3. Fever: It may be caused by decreased immunity, infection and other reasons. When the patient has a fever, the muscles of the body can produce lactic acid. When lactic acid accumulation can appear limb pain phenomenon, which is easy to cause children crying at night phenomenon. It is recommended that children crying at night go to the hospital in time, do the relevant examination to clarify the cause of the disease, follow the doctor’s instructions for treatment, to avoid delaying the condition.