Most babies under six months don’t need any vitamin supplements as they get all the nutrients they need from breast or formula milk. After six months, the current advice is for a breastfed baby who is having breastmilk as the main drink to have Vitamin A and D supplements.
Bottle fed babies on less than 600ml of formula a day need supplements, too. After a year, discuss the situation with your health visitor. Toddlers whose diets are good, and who have the chance to go outside every day, don’t need supplements (vitamin D can be processed by the body through access to sunlight).