Food insecurity is pervasive and highly seasonal in Ethiopia. In this study, we investigate the effect of seasonal food insecurity on child development. Exploiting the Young Lives Ethiopia dataset, we study the impact of in utero exposure to seasonal food insecurity on cognitive development for children of age 8 up to 12. We find that at age 8 in utero exposure to food insecurity shocks negatively, although insignificantly, affects cognitive development. But, at age 12, such exposure significantly reduces cognitive development. In utero exposure to seasonal food insecurity translates into a loss of 0.52 standard deviations in maths achievements score. Exposure during the first and second trimesters of pregnancy are found to have stronger detrimental effects. We also find stronger effects for boys.