Fluid therapy is the most widely used medical treatment, with indications and risks that are important to know. Its indication in the pediatric perioperative period has continuously changed with the upward understanding of the physiology of newborns, infants and children, as well as in the knowledge of the composition of the different fluids available for use in this patient's population. This is evident in the various existing guidelines on this topic. It is important to consider the preoperative fasting of our patient, which must be decreased to the maximum. We must differentiate the two objectives of fluid therapy: maintenance and replacement fluid therapy. The latest recommendations on maintenance fluid therapy indicate preferring the use of balanced solutions, and if not having these, preferring lactate ringer serum by adding glucose for a concentration of 1-2.5%, especially in patients with a higher risk of hypoglycemia. On the other hand, in replacement fluid therapy, it should always be started with crystalloids preferring isotonic balanced solutions of electrolytes. The use of colloids is controversial given the scarce scientific evidence in pediatric patients. Finally, when indicating blood products, the risks associated with transfusion should always be considered, however, we should also consider the threshold of hematocrit and platelets to transfuse if necessary, and calculate the maximum volume of blood loss allowed to be transfused.