Iron deficiency has been associated with heart failure severity and mortality in children and adults. Intravenous iron therapy has been associated with improved outcomes for adults with heart failure. However, little is known about its impact and safety in children. We performed a single-centre review of all intravenous iron sucrose infusions prescribed to hospitalised patients ≤ 21 years of age with a primary cardiac diagnosis from 2020 to 2022. Ninety-one children (median age 6 years, weight 18 kg) received 339 iron sucrose infusions with a median dose of 6.5 mg/kg [5.1 mg/kg, 7.0 mg/kg]. At initial infusion, the majority (n = 63, 69%) had CHD, 70 patients (77%) were being managed by the advanced cardiac therapy team for heart failure, 13 (14%) were listed for heart transplant, 32 (35%) were on at least one vasoactive infusion, and 5 (6%) were supported with a ventricular assist device. Twenty infusions (6%) were associated with 27 possible infusion-related adverse events in 15 patients. There were no episodes of anaphylaxis or life-threatening adverse events. The most common adverse events were hypotension (n = 12), fever (n = 5), tachycardia (n = 3), and nausea/vomiting (n = 3). Eight of 20 infusion-related adverse events required intervention, and two infusions were associated with escalation in a patient’s level of care. Following intravenous iron repletion, patients’ serum iron, serum ferritin, transferrin saturation, and haemoglobin increased (p < 0.05 for all). In children hospitalised with cardiac disease, intravenous iron sucrose repletion is safe and may improve haemoglobin and iron parameters, including transferrin saturation and ferritin levels.