The american academy of pediatrics recommends all infants be given iu of vitamin d per day until they are consuming that much from food.

Research has shown that The American Academy of Pediatrics have recommendations that all children receive 400 IU per day of vitamin D from 0 through their teenage years as breastfed children are at higher risk since breast milk contains almost no vitamin D.

They use the si unit, or metric system its all the same thing