This thesis aims to address a central question in cognitive science: how we reason about our own and others’ cognition. Representing the self and others as distinct individuals is a fundamental epistemological feature of being human; the richness of these representations underlies our ability to tackle our own objectives and to understand the goals of others. Yet there is much debate about the metacognitive abilities of young children, in particular the extent to which children’s estimations of their own and others’ knowledge are accurate, whether children’s beliefs about their own and others’ cognition are influenced by the evidence they observe, and if these beliefs inform effective self-directed learning. I investigate these questions, examining metacognition and its relationship to learning in 3- to 8-year-olds. Chapter 1 provides an overview of metacognition regarding the self and others. Chapter 2 considers whether young children expect others will learn rationally from evidence. We find that by age 4.5 years, children have a nuanced understanding of how evidence and prior beliefs interact to yield new knowledge. Chapter 3 investigates how children’s exploration is influenced by representations of task difficulty, as indexed by the discriminability of alternative hypotheses. We show that there is a precise quantitative relationship between uncertainty and information seeking. Chapter 4 considers how preschoolers use social comparison information to calibrate their self-directed learning, demonstrating that when a task is within children’s zone of proximal development, observing evidence that peers perform better increases one’s own persistence. Chapter 5 asks how 3- to 5-year-olds integrate representations of their own and others’ abilities when allocating roles across contexts. This work demonstrates that children consider who is best suited for a task based on relative ability. Across all four chapters, the results of these studies demonstrate that children have a sophisticated understanding of their own and others’ knowledge and skills. In addition, children use information about others to effectively direct their own learning and problem solving. I end by arguing that young children have a theory of individuals’ characteristics, of which reasoning about the self is a special case. Taken together, these studies illustrate the importance of considering how reasoning about the self and about others are integrated and are fundamental to our human intelligence