The goal of this chapter is to highlight the powerful influence that our experience can exert on the brain during development. We begin by providing an overview of brain development, an ongoing process that begins shortly after conception, and ends in early adulthood. We will then discuss how and when experience influences the developing brain. We provide several examples in different domains - sensory, language, memory, and social and emotional development - illustrating the astonishing plastic ability that the brain exhibits throughout development. These examples will provide two critical bits of information: first, a normative experience during the first years of life is essential for brain anatomy and brain function to develop normally; second, each neural circuit is differentially sensitive (malleable or vulnerable) to experience as it matures. Therefore the same experience will not have the same impact during infancy, childhood, or adolescence. In the same way, therapeutics and interventions aimed to alleviate deleterious environmental effects have to be applied during specific times of development, depending on the neural circuit and the function targeted in order to be optimally effective. Overall, we hope this chapter will promote the importance of developmental neuroscience research to better understand the needs of our children and their vulnerabilities, and in so doing to improve child policies and intervention programs.