Mediterranean Diet Adherence, Weight Status, and Self-Concept in Primary Schoolchildren in Melilla, Spain: A Comparison of Two Independent Cohorts Assessed in 2018 and 2024

Background/Objectives: Comparing children’s dietary patterns, weight status, and self-concept across assessment periods may provide a broader perspective on child health. This study aimed to examine differences in Mediterranean diet adherence, weight status, and self-concept between two independent cross-sectional cohorts of primary schoolchildren assessed in 2018 and 2024. Methods: This comparative cross-sectional study included 419 primary schoolchildren attending a single school in Melilla, Spain, recruited through convenience sampling in 2018 (n = 188) and 2024 (n = 231). Body mass index (BMI) was used to classify weight status. Mediterranean diet adherence and self-concept were assessed using the Mediterranean Diet Quality Index for Children and Adolescents (KIDMED) and the Form 5 Self-Concept (AF5) Questionnaire, respectively. General linear and multinomial logistic regression models examined between-cohort differences adjusted for age and sex. Results: Mean BMI did not differ significantly between cohorts, and adjusted KIDMED scores did not differ significantly. Weight-status distributions differed before adjustment, but the overall adjusted association with assessment year was not statistically significant. Social, emotional, and family self-concept scores were lower in 2024 after adjustment (mean differences [2024 − 2018]: −0.493, −0.641, and −0.609, respectively; all p < 0.001), with similar sensitivity estimates. No KIDMED item survived Bonferroni correction. Exploratory analyses suggested school-grade interactions for some self-concept outcomes, but no statistically significant sex interactions. Conclusions: Children assessed in 2024 had lower social, emotional, and family self-concept scores after adjustment, despite no statistically significant differences in mean BMI or overall diet adherence. Adjusted evidence of weight-status differences was less consistent. These findings support considering psychosocial, anthropometric, and dietary indicators together when monitoring child health in similar school settings.