Acute severe colitis (ASC) is a relatively frequent manifestation in children with ulcerative colitis and one of the few emergencies in paediatric gastroenterology. A standardized proactive approach based on tight monitoring and timely medical and surgical interventions may improve patients' outcomes. We aimed to update the previous ASC guidelines using detailed recommendations and practice points, based on a systematic review of the literature and consensus of experts. These guidelines update is a joint effort of the European Society of Paediatric Gastroenterology, Hepatology and Nutrition and the European Crohn's and Colitis Organization. A systematic search was performed in Pubmed Ovid Medline, Embase and Cochrane databases using 13 predefined PICO (patient, intervention, comparison, outcomes) based questions and 30 non-PICO based questions. Grading methodology was based on the Oxford Centre for Evidence-Based Medicine-Levels of evidence. The questions were addressed by working subgroups following an iterative consensus voting process, including three online voting meetings and one face-to-face meeting. A total of 36 recommendations and 72 practice points were endorsed with a consensus rate of at least 88% for all statements, regarding initial evaluation, monitoring, medical and surgical treatment of ASC in children. Several topics have been revised since the previous 2018 guidelines and differ from corresponding published adult guidelines. These guidelines present a comprehensive overview of the management of ASC in children, offering practical recommendations and practice points aiming to standardize clinical and surgical treatment and improve outcomes of this severe scenario.