The difference between AD and D3, AD refers to vitamin AD, which includes both vitamin A and vitamin D. D3 only includes vitamin D, without vitamin A. Vitamin D has an important role in children’s bones, teeth, nervous system and immune function. Vitamin A is essential for the development of children’s skin mucous membrane and digestive system functions, especially for children under two years old, and our national consensus of child health experts requires vitamin AD with supplementation. Because from the nutritional composition, whether eating breast milk or formula, the composition of these two vitamins are insufficient, from half a month after birth need to be supplemented in accordance with the physiological needs, at least 2-3 weeks of age before stopping, normal children can supplement the physiological needs. Some children may need more vitamin D due to various disease states, or premature birth, twin births, and other special circumstances, these cases need to be under the guidance of a doctor, choose the appropriate dose of supplementation.