Aim. To study the effect of ω-3 polyunsaturated fatty acids (PUFAs) on the cognitive functions of children with lipid metabolism disorders of different ages. Materials and methods. The study included 87 children aged 6 to 17 years who had not previously received ω-3 PUFA supplements. All subjects were tested twice, with an interval of 6 months, to determine the ω-3 erythrocyte index by gas chromatography-mass spectrometry and to study attention span and focusing using the correction task method (Bourdon test). The cohort was randomly divided into two groups: the main group, which included 60 children who received the ω-3 supplements, and the control group, which included 27 children who did not receive any nutritional supplements. Results. In children of the main group, after receiving the Norwegian fish oil NFO® at 1000 mg for 6 months, an increase in the erythrocyte ω-3 index was observed, while in the control group, it did not change significantly. A statistically significant correlation was found between the adequacy of ω-3 PUFA and the attention span and focusing. Conclusion. The results of the study showed the effectiveness of ω-3 PUFA supplementation at 1000 mg/day for 6 months and confirmed the positive effect of ω-3 PUFA on the cognitive sphere of children and adolescents. High-quality food supplements with ω-3 PUFAs at 1000 mg/day can be recommended to develop intellection, memory, and attention span and focus in children and adolescents.