Natural languages distinguish between telic predicates that denote events leading to an inherent endpoint (e.g., "draw a balloon") and atelic predicates that denote events with no inherent endpoint (e.g., "draw balloons"). Telicity distinctions in many languages are already partly available to 4-5-year-olds. Here, using exclusively nonlinguistic tasks and a sample of English-speaking children, we ask whether young learners use corresponding temporal notions to characterize event structure--that is, whether children represent events in cognition as "bounded" temporal entities with a specified endpoint or "unbounded" temporal units that could in principle extend indefinitely. We find that 4-5-year-old children in our sample compute boundedness during an event categorization task (Experiment 1) and distinguish event boundedness from event completion (Experiment 2). Furthermore, 4-5-year-olds in our sample evaluate interruptions at event endpoints versus midpoints differently--but only for events that are construed as bounded, presumably because in such construals, events truly culminate (Experiment 3). We conclude that young children represent events in terms of foundational and abstract temporal properties. These properties could support the acquisition of linguistic aspectual distinctions and further scaffold the way children conceptualize and process their dynamic experiences.