Background: Oxidative stress is associated with the pathogenesis of epilepsy. Long-term treatment with anti-seizure medications (ASMs) may reduce antioxidant levels, which consequently impairs the brain’s ability to counteract oxidative damage. This study aimed to assess the concentrations of selected antioxidants (i.e., glutathione, retinol, and α- and γ-tocopherols) in children with epilepsy treated with polytherapy. Methods: The study included 21 children with epilepsy treated with ≥2 ASMs for at least 6 months (mean age 7.1 ± 4.4 years) and 23 control children without epilepsy (mean age 7.4 ± 3.9 years). Both groups were recruited at the Department of Pediatric Neurology, the Medical University of Silesia in Katowice (Poland). The concentrations of glutathione, retinol, and α- and γ-tocopherols were determined in blood serum by HPLC. The antioxidant levels were compared between sex and age subgroups of individuals with epilepsy. Results: In the group of individuals with epilepsy, the percentage of females was 38% and in the control group it was 30%. There were no differences in antioxidant levels between female and male individuals with epilepsy, nor between younger epileptic children (0–6 years) and older children (>6 years). Individuals with epilepsy had significantly lower glutathione levels than the control group (1.5 ± 0.3 µmol/L vs. 2.4 ± 1.2 µmol/L, respectively, p < 0.001). In turn, the ratios of both α-tocopherol/glutathione and γ-tocopherol/glutathione were higher in individuals with epilepsy than in the control group (p = 0.042 and p = 0.004, respectively). Individuals with epilepsy taking ASM combinations other than valproic acid (VPA) and levetiracetam (LEV) had a lower level of both retinol and glutathione than individuals on VPA and LEV treatment (for retinol 0.44 ± 0.13 µmol/L vs. 0.6 ± 0.1 µmol/L, respectively, p = 0.047, and for glutathione 1.3 ± 0.3 µmol/L vs. 1.8 ± 0.3 µmol/L, respectively, p = 0.003). In the individuals with epilepsy, the level of α-tocopherol decreased with age (r = −0.505, p = 0.019). In turn, in the control group, the levels of retinol and γ-tocopherol increased with age (r = 0.573, p = 0.004 and r = 0.461, p = 0.027, respectively). Conclusions: Glutathione levels significantly differed between children with and without epilepsy. The concentration of α-tocopherol decreased with age in pediatric individuals with epilepsy. The levels of both retinol and glutathione were higher in individuals with epilepsy taking VPA and LEV treatment compared to individuals on ASMs combination other than VPA and LEV.