The codevelopment of children's general causal reasoning and their causal reasoning of illness transmission

Identifying how children develop causal understanding of illness transmission is key to fostering effective health behaviors and preventing the spread of contagious diseases. Previous research has shown that children struggle to grasp the invisible nature of germs, complicating their ability to form accurate causal explanations about illness transmission. In light of these challenges, this study examines how causal reasoning develops with age in the context of contagion and contagion-irrelevant domains. Using an online study platform, we presented participants (N = 108, Ages 4-8, North American) with a series of animated vignettes in which four characters were exposed to illness with varying degrees of (a) duration of exposure to a sick individual, (b) proximity to a sick individual, and (c) number of transfers of germs between sick individual and target. In addition, children were presented with three analogous control (contagion-irrelevant) causal reasoning vignettes that mirrored transmission principles of (a) duration, (b) proximity, and (c) number of transfers in nongerm, visible scenarios. Causal reasoning scores increased with age for both contagion-relevant and control vignettes, with contagion causal reasoning lagging behind general causal reasoning ability. The difference between children's performance on control and germ vignettes suggests that the challenges children experience reasoning about germ transmission go beyond understanding transmission processes in general, and may reflect difficulty understanding that germs specifically follow similar mechanisms of transmission. Our results underscore the critical need for targeted educational interventions, especially those focusing on causal mechanisms, to help improve children's reasoning about germs and illness transmission. (PsycInfo Database Record (c) 2026 APA, all rights reserved).