SOS/VOD is a life-threatening complication of hematopoietic stem cell transplantation, especially in children, with incidences reaching up to 15–20%. Despite efforts, SOS/VOD remains unpredictable with significant morbidity and mortality. High-risk criteria are clearly defined, and the pediatric EBMT diagnostic criteria have improved sensitivity, reducing treatment delays and enhancing outcomes. A meta-analysis combining retrospective and prospective studies found a risk ratio of 0.30 for SOS/VOD with defibrotide (DF) prophylaxis. Additionally, two prospective trials were conducted: the pediatric prevention trial (NCT00272948) and the Harmony Trial (NCT02851407), involving adults and children, with primary outcomes of incidence and SOS/VOD-free survival, respectively. The trials produced conflicting results regarding the effectiveness of prophylactic DF. Despite significant limitations of the Harmony trial, a direct healthcare professional communication (DHPC) from the European Medicines Agency (EMA) advised against prophylactic DF. This recommendation has serious consequences for children, especially infants, who are among the most vulnerable groups receiving HSCT. Therefore, a panel of experts issued guidelines for children at high risk for SOS/VOD, in which DF prophylaxis is considered justified. These guidelines include a weighted scoring system based on all relevant high-risk criteria to predict SOS/VOD, supporting decisions regarding the use of prophylactic DF in children.