DescriptionUnderstanding time is essential for people to be able to structure their own experience. Children’s understanding of time develops as they become more and more capable of talking, thinking, and reasoning about time. How does temporal reasoning ability develop in young children? What are the cognitive processes required by temporal reasoning, reasoning about causal relations, and reasoning about sequential relations? This dissertation investigated 3- to 6-year-olds’ temporal causal reasoning and temporal sequential reasoning with two child-familiar contexts, changes in possession and changes in location over time. Study 1 investigated temporal causal reasoning; children were asked to reason about the possession changes given a gain or a loss event happening in the past or in the future. Five experiments were conducted to explicate the cognitive processes required in temporal causal reasoning and also to delineate the developmental trajectory of this ability in young children. Results showed that 3- and 4-year-olds’ temporal reasoning ability was very limited, although they were capable of some temporal reasoning processes, such as matching and identifying outcomes. Children from age 5 were able to reason about causes and effects from different time points, and this ability became even more proficient when children were 6. Study 2 investigated temporal sequential reasoning; children were asked to reason about location changes given a predictable movement sequence through space. Two experiments were conducted to examine children’s reasoning about spatial changes over relational temporal sequences (e.g., before and after) and their reasoning about spatial changes over deictic temporal sequences (e.g., yesterday and tomorrow). Results showed that the left-to-right linear representation of time was intuitive to children as young as 3. Compared to the unconventional right-to-left temporal spatial mapping, left-to-right temporal spatial mapping facilitates children’s temporal sequential reasoning.