Tracheostomy is increasingly performed in children for upper airway anomalies. Here, an 18-month-old child (height 84.1 cm, weight 12.5 kg) presented to the emergency department with dyspnea, stridor, and chest retraction. However, exploration of the airways using a bronchoscope failed due to subglottic stenosis. Therefore, a surgical tracheostomy was successfully performed with manual mask ventilation. However, pneumomediastinum was found in the postoperative chest radiograph. Although an oxygen saturation of 99% was initially maintained, oxygen saturation levels dropped, due to sudden dyspnea, after 3 hours. A chest radiograph taken at this time revealed a left tension pneumothorax and small right pneumothorax. Despite a needle thoracostomy, the pneumothorax was aggravated, and cardiac arrest occurred. Cardiopulmonary-cerebral resuscitation was performed, but the patient was declared dead 30 minutes later. This study highlights the fatal complications that can occur in children during tracheostomy. Therefore, close monitoring, immediate suspicion, recognition, and aggressive management may avoid fatal outcomes.