Background: Critically ill paediatric patient (CIPP) care may be required in the adult intensive care unit (aICU) of hospitals in cases where there is no paediatric intensive care unit (pICU) or when the pICU bed capacity is insufficient. Objectives: This is a retrospective evaluation of CIPPs who were accommodated in aICUs over the last 10 years to determine the type of hospital admission, indications for hospitalization, presence of comorbidities, treatments, causes of mortality, and effects of these parameters on mortality. Methods: We retrospectively analysed the medical records of 600 patients aged 28 days to 17 years who had been cared for at least 24 hours in aICUs between 2011 and 2021. Results: The average age of the CIPPs ((252 female (42%), 348 male (58%)) was 6 (7.4 ± 5.4) years. The mortality rate was 14.7%, and trauma (31.8%) was the most common cause of mortality, followed by respiratory diseases and septic shock. The independent risk factors found to be associated with mortality were as follows: Lower age, admission to ICUs from emergency departments of hospitals, higher Pediatric Risk of Mortality III and Pediatric Logistic Organ Dysfunction II scores, duration of hospital stay and of mechanical ventilation, vasopressor/inotropic agent requirement in the first 24 hours, higher total transfusion requirement, presence of nosocomial infection, thrombocytopenia, and lower haemoglobin level. Conclusions: It is important to achieve the best results and better outcomes for CIPPs in pICUs. However, a significant proportion of CIPPs currently hospitalized in aICUs are admitted with trauma. A close follow-up of mortality scores and clinical parameters in the early period of CIPP care in the aICU is critical as some mortality risk factors are preventable.