<p>Childhood aggression emerges from interactions between children’s emotional reactivity and their social environments, yet developmental models rarely examine how parental physiological responses shape the behavioral meaning of children’s biological sensitivity. We investigated whether parent–child parent and child physiological responding during emotional processing is associated with distinct forms of childhood aggression. One hundred seventy-six parent–child dyads completed an affective viewing task involving distress, threat, victimization, and positive stimuli while electrodermal activity was recorded in both parents and their children. Measures of callous–unemotional traits and parental sensory processing sensitivity were also obtained. Hierarchical regression analyses showed that children’s distress-related physiological reactivity predicted overt reactive aggression only as a function of parental physiological responsiveness. Specifically, higher child reactivity was associated with lower aggression when parental physiological responses were low but with higher aggression when parental reactivity was elevated. Comparable effects were not statistically significant for proactive or relational aggression or for other emotional conditions. These findings indicate that children’s biological sensitivity acquires behavioral significance within emotion-specific parent–child physiological contexts, highlighting interpersonal biological pathways linking parenting processes and childhood aggression. Results underscore the importance of considering parental regulation processes when examining how children’s emotional reactivity contributes to aggressive behavior.</p>