Although thermal conditions influence the development of living organisms in a wide variety of ways, this topic has been recently ignored in humans. This paper reintroduces thermal conditions as a topic of importance for developmentalists by presenting an example of how thermal conditions are hypothesized to influence a particular developmental system. Specifically, several literatures support the theory that chronic exposure to heat stress adversely influences individual cognitive development in children. We theorize that chronic heat stress reduces active interaction with environmental stimuli. Reduced environmental experience results in fewer experience-produced brain changes than would have occurred in a neutral thermal environment. Because many children worldwide develop in thermally stressful environments for at least several months of the year, this topic has real-world implications for human development. Finally, the broader intention of this paper is to encourage developmentalists to consider the influence of a wide variety of thermal conditions on human development.