Almost 300 million children under five years of age are anaemic worldwide. International policymakers recommend universal distribution of iron-based interventions – either iron supplements or iron-containing multiple micronutrient powders – to alleviate the burden of anaemia in young children. When considering whether to implement universal iron interventions, it is essential to balance the putative benefits with possible risks. The key rationale for deploying universal iron interventions to reduce anaemia in young children is to improve development, growth and wellbeing. Whilst plausible, few randomised controlled trials of iron interventions have carefully assessed these outcomes. There is currently inadequate evidence to support the hypothesis that universal iron interventions (either as iron supplements or multiple micronutrient powders) provide benefits on functional child health outcomes. Conversely, several important randomised controlled trials have found that when universal iron interventions are given to all children in a population, they may increase infection risk. Other possible risks of iron interventions have not yet been extensively described but include a risk of iron overdose and long-term iron loading in high-risk individuals. Identifying whether universal iron interventions provide a net benefit or harm to populations is challenging.