Children and pregnant women are vulnerable populations lacking clinical data to guide drug dosing. For children, over the past 15 years, the knowledge gap in pharmacokinetic, safety, and efficacy data has been narrowed as a result of the use of innovative clinical trial designs, minimal risk research methods, increased understanding of developmental pharmacology, multidisciplinary research teams, increased clinical pharmacology expertise and training, collaborative research networks, and critical legislative changes. This progress has not been observed to a similar degree for pregnant women. These two populations, however, share similar drug development challenges and, therefore, lessons learned in pediatric clinical trials can be leveraged to advance drug development in pregnant women.