Objective: This study aimed to evaluate the predictive value of complete blood count-derived inflammatory indices for metabolic syndrome (MetS) in children and adolescents with obesity. Methods: A cross-sectional study was conducted from January to March 2025. Participants aged 5–17.9 years with obesity were classified into MetS and non-MetS groups according to the International Diabetes Federation pediatric criteria. Participants were further stratified by pubertal stage into prepubertal, pubertal, and postpubertal groups. Results: A total of 343 subjects with obesity (median age: 13.3 years; interquartile range: 4.74) were studied. MetS was diagnosed in 97 individuals (28.2%). Those with MetS had significantly higher body mass index (BMI), waist circumference, hip circumference, waist-to-height ratio, blood pressure, triglycerides, fasting plasma glucose, insulin levels, and Homeostasis Model Assessment of Insulin Resistance, and lower high-density lipoprotein cholesterol (HDL-C) compared with participants without MetS. Notably, inflammatory markers, including the neutrophil-to-HDL-C ratio, lymphocyte-to-HDL-C ratio, monocyte-to-HDL-C ratio, and platelet-to-HDL-C ratio (PHR), were also elevated in the MetS group. Correlation analyses revealed significant associations between these indices and various cardiometabolic parameters, including insulin resistance markers. Logistic regression analysis identified BMI and PHR as the most robust independent predictors of MetS. Additionally, stage-specific cutoff values for these markers were established according to pubertal development. Conclusions: The study shows that certain novel inflammatory indices are elevated in children with MetS and are significantly correlated with key cardiometabolic risk factors. These results suggest that such markers could serve as practical tools for early detection of cardiometabolic risk in youth with obesity.