Antithrombin (AT), a glycoprotein, plays a key role in anticoagulation by inhibiting coagulation proteases. It is also the primary mediator of heparin’s anticoagulant effect, with heparin binding amplifying AT activity up to 1000-fold. Deficiency in AT contributes to a hypercoagulable state associated with adverse clinical outcomes, including morbidity and mortality. Hereditary AT deficiency (hATD) is a rare autosomal dominant disorder caused by mutations in the gene encoding AT (SERPINC1), resulting in decreased AT levels or activity. As the most thrombogenic inherited thrombophilia, hATD confers a lifetime venous thromboembolism (VTE) risk of up to 85%, with similar annual VTE incidence in both pediatric and adult patients. Management of hATD often includes AT concentrate (ATc) therapy in high-risk clinical settings. Although ATc has a long history of use in adults, pediatric use has been largely off-label and guided by extrapolation from adult data. In August 2025, the U.S. Food and Drug Administration (FDA) approved an expanded indication for antithrombin III concentrate (human) to include pediatric patients with hATD, representing the first product specifically approved for this population. In light of this recent shift in the treatment landscape, this review provides a timely synthesis of the current clinical understanding and evidence-informed strategies to optimize AT therapy in the management of pediatric hATD.