Vitamin D3 is taken from 15 days after birth and can usually be stopped at around 3 years of age. Vitamin D3 is a fat-soluble vitamin that has the ability to promote calcium synthesis and absorption, and when taken during infancy and early childhood, it helps prevent rickets in children. Usually, babies start taking vitamin D from about 15 days old. Generally, vitamin D3 can be taken routinely until the child is about 3 years old to stop, because this stage of the young children, from the three meals a day from the food to obtain enough calcium for its normal growth and development, outdoor activities are gradually increased, vitamin D3 usually do not need to take additional supplements. It is worth noting that after the age of 3, if your child shows signs of calcium deficiency or other abnormalities of vitamin D deficiency, it is recommended that you take your child to a specialized hospital for a comprehensive examination, and continue to take vitamin D3 supplements under the guidance of your doctor.