Background <p>Household food insecurity remains a critical challenge in Ethiopia. While maternal education and family size are considered key determinants, their independent and interactive effects are not well understood in urban settings.</p> Objective <p>This study assessed the associations between maternal education, family size, and household food insecurity among households with young children in Harar City, eastern Ethiopia, testing the hypothesis that maternal education moderates (buffers) the relationship between family size and food insecurity.</p> Methods <p>We conducted a secondary analysis of cross-sectional data from 542 households. Food security was measured using the Household Food Insecurity Access Scale (HFIAS). Hierarchical multivariable linear regression was used, incorporating an interaction term between family size (continuous) and maternal education (categorical: none, primary, secondary+) to test for moderation. Models adjusted for wealth index and maternal age.</p> Results <p>Food insecurity was highly prevalent (79.2%). The interaction between maternal education and family size was not statistically significant (<i>p</i> = 0.561), rejecting the moderation hypothesis. In the final adjusted model, only maternal age was significantly associated with higher food insecurity (β = 0.013, 95% CI 0.001–0.025, <i>p</i> = 0.032). Family size, maternal education, and wealth index were not independent predictors. The overall model explained little variance (R² = 0.030).</p> Conclusion <p>In this urban setting, maternal education did not modify the relationship between family size and food insecurity, and neither was an independent predictor after adjustment. The positive association with maternal age warrants further investigation. The minimal explanatory power of standard socioeconomic variables suggests food insecurity in this context is driven by a broader range of unmeasured structural, economic, or environmental factors, necessitating comprehensive intervention strategies.</p>