Children's early interactions with adults during the first three years of life are instrumental in the development of their language, cognitive, and social skills, which in turn are strongly related to later achievement and success into adolescence. Early childhood professionals working with infants and toddlers need to understand children's capacity to learn and how to promote young children's development and learning. Prior research about how professional development (PD) can change teacher beliefs, knowledge, and practices has mostly focused on preschool and school-age children. Those caring for infants and toddlers often have less access to and fewer opportunities for sustained and systematic PD. The first few years of a child's life are especially important in brain development. Thus, there is a clear need to examine the potential benefits of different forms of PD specifically for caregivers serving infants and toddlers. The goal of this brief is to describe differences in beliefs, knowledge, and practices of infant and toddler caregivers from fall 2018 to spring 2019--before and after implementation of the We Grow Together (WGT) PD system.