Background <p>Cognitive development is associated with diet, activity, sleep, metabolic health, and socioeconomic status. However, evidence remains limited, as most studies have focused on clinical groups or single factors. We examined the combined associations of these variables with cognitive function in school-aged children from the general population.</p> Methods <p>We evaluated 170 school-aged children from a population-based cohort (mean age 6.33 ± 0.03 years; 49% female). Children were evaluated after an overnight fast (&gt;8 h), and anthropometric, metabolic, and socioeconomic variables were evaluated. Diet and physical activity were assessed using validated questionnaires (Vioque FFQ and enKid). Cognitive function was assessed using NEPSY-II and TONI-2 subsets. Correlation and regression analyses were performed.</p> Results <p>Cognitive function was positively associated with Mediterranean diet adherence, sleep duration, socioeconomic status, and negatively associated with ultra-processed food intake, TV viewing, and metabolic markers including insulin resistance (HOMA-IR), C-reactive protein, and gamma-glutamyltransferase (all <i>p</i> &lt; 0.05). Multivariate analyses showed that Mediterranean diet adherence (OR 2.18, 95%CI 1.08–4.40), economic status (OR 2.50, 95%CI 1.13–5.49), sleep duration (OR 2.90, 95%CI 1.42–5.92), and HOMA-IR (OR 0.47, 95%CI 0.23–0.96) as independently associated with cognitive outcomes, particularly in attention, language, and memory.</p> Conclusions <p>Lifestyle factors and socioeconomic conditions are independently associated with cognitive function in children.</p> Impact <p><UnorderedList Mark="Bullet"> <ItemContent> <p>Key message: Diet, sleep, metabolic health, and socioeconomic status are associated with cognitive function in school-aged children.</p> </ItemContent> <ItemContent> <p>Novelty: Simultaneously examines multiple factors associated with cognition in school-aged children from a population-based cohort.</p> </ItemContent> <ItemContent> <p>Impact on cognition: Mediterranean diet adherence, sleep duration, and metabolic health were positively associated with several cognitive domains, including attention, language, and memory.</p> </ItemContent> <ItemContent> <p>Practical use: Highlights the potential relevance of healthy lifestyles and social equity in relation to cognitive development.</p> </ItemContent> <ItemContent> <p>Broader significance: Highlights the multifactorial nature of cognitive development in children.</p> </ItemContent> </UnorderedList></p>