Purpose of reviewThe issues of fluid balance and fluid overload are currently considered crucial aspects of pediatric critically ill patients' care.Recent findingsThis review describes current understanding of fluid management in critically ill children in terms of fluid balance and fluid overload and its effects on patients' outcomes. The review describes current evidence surrounding definitions, monitoring, and treatment of positive fluid balance. In particular, the review focuses on specific patient conditions, including perioperative cardiac surgery, severe acute respiratory failure, and extracorporeal membrane oxygenation therapy, as the ones at highest risk of developing fluid overload and poor clinical outcomes. Gaps in understanding include specific thresholds at which fluid overload occurs in all critically ill children or specific populations and optimal timing of decongestion of positive fluid balance.SummaryCurrent evidence on fluid balance in critically ill children is mainly based on retrospective and observational studies, and intense research should be recommended in this important field. In theory, active decongestion of patients with fluid overload could improve mortality and other clinical outcomes, but randomized trials or advanced pragmatic studies are needed to better understand the optimal timing, patient characteristics, and tools to achieve this.