Fluid balance management in pediatric critically ill patients is a challenging task, since fluid overload (FO) in the pediatric ICU is considered a trigger of multiple organ dysfunction. In particular, the smallest patients with acute kidney injury are at highest risk to develop severe interstitial edema, capillary leak syndrome and FO. Several studies previously showed a statistical difference in the percentage of FO among children with severe renal dysfunction requiring renal replacement therapy. For this reason, in children priority indication is currently given to the correction of water overload. If this concept is so important in the critically ill small children, where capillary leak syndrome is a dramatic manifestation, it has probably been underestimated in critically ill adults and only recently re-evaluated. The present review will shortly describe nutrition strategies in critically ill children, it will discuss dosages, benefits and drawbacks of diuretic therapy, and alternative diuretic/nephroprotective drugs currently proposed in the pediatric setting. Finally, specific modalities of pediatric extracorporeal fluid removal will be presented. Fluid management, furthermore, is not only the discipline of removing water: it should also address the way to optimize fluid infusions and, above all, one of the most important fluids infused to all ICU patients with renal dysfunction: parenteral nutrition.