Optimism, briefly defined as a cognitive bias to overestimate positive future outcomes, is associated with motivational, social, and health benefits in adults. However, little is known about how optimism develops. We posit that optimism is present early and influences how children learn from and about the world around them. As children gain direct experience with event outcomes, and probabilistic reasoning improves, this bias diminishes. Further, divergent developmental trajectories may emerge such that optimism declines more steeply in children who experience more negative life events. We will test 3- to 6-year-old children from diverse backgrounds to determine whether children offer accurate or optimistic predictions about the likelihood of events occurring, misremember probabilistic outcomes optimistically, and/or prefer optimistic people. Our research addresses critical questions about early optimism, including whether optimism is expressed differently in children versus adults, environmental and familial factors affecting early optimism, and how optimism ultimately shapes and guides learning.