Purpose: Oxidized LDL cholesterol (oxLDL) has been considered as a sensor of oxidative stress (OS) in childhood obesity. We integrated and related our oxLDL existing results previously assessed in overweight/obese children to lifestyle variables to investigate OS-related lifestyle variables. Methods: 178 Caucasian children/adolescents have been evaluated and according to BMI percentiles have been classified as normal weight (BMI < 75th); overweight (BMI 75–97th) and obese (BMI > 97th). Serum oxLDL levels have been measured. The dietary habits and physical activity have been also assessed. Results: No differences between normal weight and overweight/obese children were detected according to the total score of dietary habits section. Normal weight subjects reported a higher total physical activity score (p = 0.001) compared to overweight/ obese children. No correlation between oxLDL and total dietary habits and physical activity scores was noted. Increased oxLDL in subjects drinking < 1 L/day of water (p = 0.022) and in daily consumers of chocolate drinks at breakfast (p = 0.029) was observed, while a decreased oxLDL was reported in subjects consuming a breakfast based mainly on fruits (p = 0.004). Moreover, “high-fat diet” and “always eating a dessert at the end of the meal” were correlated with increased oxLDL with a trend towards significance. As regards physical activity, no correlations were observed. Conclusions: Diet and physical activity may not have an immediate impact on OS response in children with or without obesity. Unhealthy lifestyle, including increased fat, simple sugar intake, poor water intake, emerged as external exposome predictors of OS, that may be monitored to improve health status. Level of evidence: Level III, case-control analytic studies.