National-level data on iron deficiency is not available for most countries and many rely on the prevalence of anemia as a proxy estimate, assuming that approximately 50% of anemia cases are caused by iron deficiency. Anemia, however, has multiple causal factors and the risk attributable to any one cause will depend on its relative importance in a population in relation to other causes. The present review summarizes current estimates on the prevalence of iron deficiency and anemia in children younger than 2 years and evaluates the strengths and weaknesses of currently available indicators of iron deficiency in children. Anemia prevalence is insufficient to estimate the prevalence of iron deficiency in children younger than 2 years. The methods widely used to assess iron deficiency at the population level rely on venous blood samples and are complicated and costly to implement.