Maternal weight and gestational diabetes mellitus (GDM) have significant implications for both maternal and child health. This narrative review explores the intricate relationship between maternal pre-pregnancy weight, gestational weight gain, and GDM, focusing on their short- and long-term effects on child health outcomes. The review highlights evidence linking maternal obesity and GDM to increased risks of adverse outcomes in infants and children, such as macrosomia, neonatal hypoglycemia, childhood obesity, and metabolic disorders. It also discusses the intergenerational transmission of metabolic risk, underscoring the importance of early intervention and prevention strategies in maternal healthcare. Furthermore, the review emphasizes the need for tailored approaches to managing maternal weight and GDM to mitigate potential risks and improve health outcomes for future generations. Key recommendations include promoting healthy preconception weight, monitoring gestational weight gain, and enhancing postnatal follow-up for both mothers and children. This review underscores the critical role of maternal health in shaping the developmental trajectory of offspring and highlights opportunities for healthcare professionals to reduce the long-term impact of GDM on child health.