Lupus anticoagulant (LA) is made up of heterogeneous IgG and IgM antibodies that prolong clotting times in vitro and is associated with an increased rate of both thrombosis and hemorrhage in vivo, although thrombosis is far more common. Many mechanisms of action have been explored, but none explains the coagulation abnormality of every sample tested. Binding of these antibodies to protein phospholipid complexes provides a unifying model. Antiphospholipid antibodies (APAs) are found in adult patients with a variety of disorders or as an isolated finding. The association of LA and anticardiolipin antibodies (ACAs) with thrombosis in adults has been established, although there is no test as yet to predict thrombotic risk for an asymptomatic affected individual. The presentation of thrombosis with postinfectious APA is uncommon in adults. Children who present with thrombosis and LA are found to have underlying disorders similar to those of adults. Although the presentation of thrombosis in children with postinfectious LA is rare, the association is established. LA-positive children with thrombosis have manifested a severe acquired deficiency of protein S; LA-positive children with hemorrhage have manifested an acquired deficiency of prothrombin. The association of thrombosis with ACA-positive children has been reported. Further work to determine the epidemiology, mechanism of action, and thrombotic potential of APA in children is warranted to better understand, prevent, and treat thrombotic and hemorrhagic complications.