Advances in sequencing technology and increasing recognition of the importance of our microbial world have led to unprecedented discoveries in recent years with respect to the human microbiome. We have begun to appreciate the degree to which the human microbiome is dynamic, can be highly personalized, and may be shaped by a variety of factors, including life stage. We also recognize that human-associated microbial communities have the potential to play important roles with respect to development, immunity, and health outcomes later in life. Given the potential importance of early-life exposures, establishing a baseline understanding of the pediatric microbiome is essential. Here we will address the state of the science regarding microbiome development in infancy and childhood and discuss recent findings related to the pediatric microbiome.