Babies are born with some stores of iron which last for about six months. To some extent, the baby's iron levels depend on the mother having enough iron during pregnancy. Premature infants sometimes have low iron stores. For the first six months of life, breast milk will supply plenty of well-absorbed iron. Formula milks have added iron and researchers try to find the type of iron that will be absorbed from formulas best.
None matches that from breast milk.
After six months of age, all babies, including those that are still being breast-fed, need foods that will supply iron. The most obvious one is meat because it is high in iron and its iron is well absorbed. As a bonus even a small amount of meat, fish or chicken in a meal will improve the absorption of non-haem iron from other foods, so these are worthwhile foods to include in a baby's diet. Babies should not be given solid foods before about 6 months of age. After that time, they are usually started on iron-fortified baby rice cereal and some pureed fruits and vegetables.