Common clinical symptoms of vitamin D deficiency in infants and young children: night terrors, irritability, night sweats, anorexia, rickets, low immunity, crying, easy sweating, occipital baldness, late and uneven teething, hand and foot twitching, square skull, O-legged or X-legged. Causes of vitamin deficiency in infants and children: 1, breastfeeding: exclusive breastfeeding history without sunlight or vitamin D supplementation is an important risk factor for vitamin D deficiency in infants. 2, premature birth: low reserves of vitamin D in the fetal period, the demand increases compared to full-term infants. 3. Fetal origin: derived from inadequate vitamin D levels in the mother during pregnancy. The role of vitamin D supplementation in infancy and early childhood: 1, to promote the absorption of calcium 2, the role of bones and teeth, to promote growth and bone calcification, to prevent rickets 3, to improve immunity to infectious diseases 4, to promote the development of brain function and behavior in children 5, to prevent and control asthma and eczema in childhood 6, to reduce the occurrence of type I diabetes 7, to reduce the occurrence of cardiovascular disease in adulthood Recommended daily intake of vitamin D3: 0 -6 months: 300 mg 7 months-12 months: 400 mg 1-3 years: 600 mg 4-6 years: 800 mg 7-9 years: 800 mg 10-14 years: 1000 mg 14-18 years: 1000 mg