Early diagnosis of postoperative complications leads to timely surgical interventions, on which the outcome of the disease depends. This also applies to postoperative intra-abdominal complications, especially in childhood, when the progression of peritonitis is fleeting, and many defense mechanisms are immature and depressed. Timely evacuation of pus from the abdominal cavity leads to a decrease in endotoxicosis, the main component in the pathogenesis of the toxic-septic process, and to a significant improvement in the results of treatment of the disease.