Although prenatal glucocorticoid exposure may impair fetal growth, evidence regarding maternal oral corticosteroid (OCS) use and long-term child growth remains limited. We conducted a nationwide cohort study using the Korean National Health Information Database linked to child health screening data. The study included liveborn children and their mothers from April 2011 to December 2022. Exposure of interest was maternal filling of 1 or more OCS prescriptions during pregnancy. The primary outcome was longitudinal height-for-age Z-score (HAZ) measured at 7 examinations between 4 and 71 months of age. Growth trajectories were modeled using linear mixed-effects models. Sibling analyses were conducted to account for shared familial confounders. Among 3,253,902 liveborn children, 3,004,048 (mean [SD] maternal age, 32.4 [4.3] years) met the eligibility criteria, including 215,083 (7.2%) prenatally exposed to OCS. Compared with no exposure, prenatal OCS exposure was associated with lower HAZ during infancy (estimated mean difference at 4 months, −0.134; 95% CI −0.139 to −0.129 in the full cohort; −0.141; −0.150 to −0.131 in the sibling cohort). The association attenuated over time, with no clinically meaningful difference by 72 months (estimated mean difference, −0.015; −0.020 to −0.009 in the full cohort; 0.011; 0.000 to 0.023 in the sibling cohort). These findings suggest that prenatal OCS exposure is unlikely to have a substantial long-term effect on child linear growth.