Three-year-old babies do not sleep at night may be caused by environmental factors, hunger, calcium or vitamin D deficiency and other reasons. 1. Environmental factors: three-year-old babies do not sleep at night may be caused by environmental factors, due to the sleep environment is noisy and bright light, there may be the phenomenon of the baby does not sleep at night or fall asleep after waking up. 2. Hunger: three-year-old babies do not sleep at night may be caused by hunger, because the baby does not eat enough before going to bed, resulting in the phenomenon of hunger, and therefore may not sleep at night. 3. Calcium or Vitamin D deficiency: In case of calcium deficiency, it may cause the baby’s sympathetic nerves to be excited, thus resulting in the phenomenon of not sleeping at night. Three-year-old babies do not sleep at night, there may be other reasons, it is recommended to go to the hospital in time to improve the examination to clarify the cause of the disease, under the guidance of the doctor to give targeted treatment or treatment.