 Neonates and infants aged less than 6 months who pass the screen of in- and exclusion criteria, who have been treated for at least five days with heparin and or VKA for confirmed symptomatic or asymptomatic arterial or venous thrombosis are eligible for the study. Study treatment consists of a 7-day treatment with an age- and body weight-adjusted three times daily, approximately 8 hours apart oral rivaroxaban dosing to achieve a similar exposure as that observed in adults treated for venous thromboembolism VTE with 20 mg rivaroxaban once daily. Rivaroxaban will be provided as granules for preparation of an oral suspension 1 mgmL after re-suspension using a t.i.d. regimen with 8-hour intervals. An ultrasound will be performed before starting rivaroxaban at treatment day 1 and after the end of rivaroxaban treatment at day 8. The last dose of rivaroxaban treatment will be followed by a 30-day post study treatment period, regardless of the duration of study drug administration. After cessation of rivaroxaban, it is at the investigators discretion to continue with anticoagulants. The principal safety outcome is the combination of major and clinically relevant non-major bleeding. The efficacy outcome is the composite of all symptomatic recurrent thromboembolism and asymptomatic deterioration in thrombotic burden on repeat imaging. All suspected recurrent thromboembolism, asymptomatic deterioration in thrombotic burden on repeat imaging, deaths, as well as all episodes of bleeding will be evaluated by a CIAC. Adjudication results will be the basis for the final analyses. 