Back to reality: Children's early temporal reasoning applies to real but not hypothetical events

Time words like "yesterday" and "tomorrow" are hard for children to learn, and for researchers to study, because their referents change from day to day. For example, "yesterday" means something different on Monday and on Wednesday. This study tested 3- and 4-year-old (n = 121; 52% female; no demographic data were collected) US and Canadian children's understanding of "yesterday" and "tomorrow" using three tasks that differed in their reliance on autobiographical and hypothetical events. Results across two experiments conducted between 2023 and 2025 indicated that 3-year-olds comprehend "yesterday" and "tomorrow" when they applied to autobiographical events. However, when asked about hypothetical timelines, even some 4-year-olds struggled to demonstrate knowledge, suggesting that children's early temporal reasoning may be limited to autobiographical events, and does not extend to hypothetical events.