Infants and children are susceptible to the profound metabolic effects of critical illness. In addition, preexisting malnutrition and obesity have adverse consequences during the intensive care unit stay. Early enteral and parenteral feeding can improve nutrition deficits, but neither has been sufficiently studied to show an effect on clinical outcomes in pediatric critical care. Indirect calorimetry is a useful technique that identifies patients receiving inadequate or excessive nutrition, but this technique is underused.