Adults of mothers with gestational diabetes mellitus (GDM) have increased risk of cardiovascular (CV) disease. This cross-sectional case-control study examines the role of prenatal GDM exposure and its possible association with altered CV health in childhood. Children of mothers with GDM (C-GDM) and age- and sex-matched controls (C-Controls), recruited from the Alberta pregnancy outcomes and nutrition birth cohort (mothers recruited 2009–2012), underwent echocardiographic and other CV assessments in 2022. Primary outcome measures included left ventricular mass, systemic blood pressure, carotid intima-media thickness, aortic and peripheral arterial stiffness (pulse wave velocity), and endothelial function (reactive hyperemia). Lifestyle measures (e.g., 24 h diet recall, accelerometer-based physical activity) of mothers and children were also considered. We assessed 25 C-GDM (20 females; 17 diet-controlled, 8 insulin-treated) and 27 C-Controls (20 females without GDM) (mean age 10.9 ± 0.7 years), with comparable birth and baseline characteristics. Aortic pulse wave velocity was higher in C-GDM versus C-Controls (6.2 ± 2.6 vs. 4.8 ± 1.6 m/s, p = 0.03), and higher in C-GDM whose mothers managed their diabetes with insulin versus diet (7.9 ± 2.6 vs. 5.5 ± 2.2 m/s, p = 0.03). No other outcomes differed statistically. Mothers with GDM, but not controls, had reduced intake of less healthy foods from second to third trimesters. Intrauterine exposure to GDM may contribute to increased aortic stiffness in childhood. This association may be worse for C-GDM whose mothers require insulin rather than diet alone for glycemic control of their pregnancy, and may occur despite dietary improvements in the third trimester. Given the small sample size, additional work is needed to confirm these findings.