Infants and children can start adding vitamin D3 after birth, and their daily requirements of vitamin D3 are as follows: 1. Fetal period: pregnant women in the second trimester of pregnancy, 800-1000 IU of vitamin D per day; 2. After the baby is born: 400 IU per day; 3. Premature babies, low birth weight babies or twins: 800 IU per day within 3 months, and later 400 IU. Please combine the specific medication with the clinical, subject to the guidance of the doctor’s face-to-face consultation.