D3 for babies is generally recommended to be taken after dinner. When babies are small and have sufficient milk intake, they do not need calcium supplements and only take vitamin D3 orally. However, when the intake of milk is not sufficient and the nutrition is not good, calcium supplements can be taken, and vitamin D and calcium supplements are more effective when taken together. For full-term infants, vitamin D supplementation should be started 2 weeks after birth with a regular oral preventive dose. In the case of premature babies, low birth weight babies and twins, vitamin D supplementation should be started 1 week after birth, and the dose can be doubled at the beginning and changed to a preventive dose after 3 months, which is needed until the baby is 2 years old. If there is enough sunshine in summer, you can take your baby to increase outdoor activities and reduce the intake of vitamin D at this time.