With global warming, heat waves are becoming more frequent and intense, particularly in northern latitudes, where the pace of warming is faster. Due to its northern location, Swedish society has been built primarily to manage a cold climate, and is less prepared to manage heat, which the 2018 heat wave demonstrated. While young children are recognized as vulnerable to heat, and are reliant on preschool care, few studies have examined how the young and vulnerable people are cared for during heat waves in the institutional preschool setting. This exploratory study demonstrates how children in preschool environments are vulnerable to heat, in order to identify management needs by assessing experienced impacts and responses to the 2018 heat wave in Sweden. Empirically, the study builds on a survey completed by 33 unit heads responsible for 77 preschools in the focused municipality, and qualitative interviews with five educators and five parents, as well as temperature measurements in three selected preschools. This study shows that: (i) children and educators are exposed to both high indoor and outdoor temperatures in the preschools; (ii) both children and educators were affected by the heat wave in the preschools, and their sensitivity is deeply intertwined due to their dependency relationship, rendering a form of double sensitivity to heat; and (iii) the preschool heads and educators were unprepared to sufficiently cope with the heat wave, and organizational strategies for managing heat were lacking, indicating weak adaptive capacity. The significant exposure to heat in preschool environments, the dual sensitivity of children and preschool educators, and the low organizational readiness resulting in uncoordinated responses to reduce heat stress suggest a pronounced vulnerability to heat waves in preschools.