Level 1: What is stage 3 of infant milk powder? Infant milk powder is a special formula food suitable for babies under 1 year old. At this age, breast milk or formula milk powder can no longer meet the nutritional needs of the baby, so stage 3 milk powder needs to be used. Compared with stage 1 and stage 2 milk powder, stage 3 milk powder has protein, fat and carbohydrates.