Children between the ages of 5 and 10 years watched a videotape of a child having a routine medical exam. Embedded within the scenes were systematic variations of depicted facial affect shown by doctor and child. Measures were taken of autonomic reactions and information-processing errors in response to positive, neutral, and negative affective cues. For 5–6-year-olds, processing errors were greatest in the negative affect condition. Additionally, peak increases in heart rate (HR) and skin conductance level (SCL) were demonstrated by 5–6-year-olds in response to negative affect shown by the witnessed child; increases in HR were in turn predictive of processing errors. Older children (9–10 years) showed trends reflecting reduced processing errors in response to witnessed negative affect. It was suggested that younger children respond to salient threat cues with a “defensive” response pattern that is relatively adaptive at younger but not older ages.