The aim of this study was to determine the ability of neutrophil lymphocyte ratio (NLR) and platelet lymphocyte ratio (PLR) to predict the severity of illness as assessed by two scoring systems, namely, Pediatric Logistic Organ Dysfunction-2 (PELOD-2) and Pediatric Risk of Mortality-III (PRISM-III) and outcome. This was a retrospective cohort study wherein all critically ill children aged 1 month to 18 years admitted in the pediatric intensive care unit from January 2021 to October 2022 were included. Children with chronic systemic diseases and hematological illness were excluded from the study. Demographic details, diagnosis, PRISM-III-24 and PELOD-2 scores at admission, and outcome were retrieved from the hospital case records. NLR and PLR values were compared among high and normal PRISM-III and PELOD-2 groups as well as among survivors and nonsurvivors. A total of 325 patients with critical illness were included with a mean (standard deviation) age of 7(5) years and a male: female ratio of 3:2. The values of NLR were significantly higher among the patients with high PRISM-III (2.2 vs. 1.3, p-value = 0.006) and PELOD-2 (2 vs. 1.4, p-value = 0.015) groups compared with normal. The NLR and PLR were significantly higher among the nonsurvivors compared with the survivors (2.3 vs. 1.4, p-value = 0.013, and 59.4 vs. 27.3, p-value = 0.016 for NLR and PLR, respectively). The area under the receiver operating characteristics curve for NLR and PLR was 0.617 and 0.609, respectively. A high PLR, PRISM-III, and PELOD-2 were the factors found to be independently associated with mortality on multiple logistic regression analysis. Patients with high NLR are associated with more severe illness at admission. NLR and PLR are useful parameters to predict mortality.