I'm presuming from your question that he has iron deficiency anemia, rather than other types of anemia. It is important to try to fix the anemia. Recent studies have shown that iron deficiency anemia probably does have an effect on how well the brain works. It is felt that anemia can cause some impairment of intellectual functioning (IQ), particularly in the infant and young child because the brain is growing and developing rapidly. Significant anemia can cause your child to be more tired. Anemia also makes a child more prone to lead poisoning if there is lead in the environment, that's why it is important for him to take the iron. But while the iron supplement will help to correct the anemia, a good diet that's high in iron will help to make sure he does not become anemic again. Good sources of iron in the diet include leafy green vegetables, red meats, eggs, and iron-fortified foods.