Williams syndrome (WS) and autism spectrum disorder (ASD) are associated with atypical social-emotional functioning. Affective visual stimuli were used to assess autonomic reactivity and emotion identification, and the social responsiveness scale was used to determine the level social functioning in children with WS and ASD contrasted with typical development (TD), to examine syndrome-specific and syndrome-general features. Children with ASD exhibited the highest arousal in response to faces, with a lack of difference in autonomic sensitivity across different emotional expressions, unlike in WS and TD. The WS group demonstrated unique deficits in identifying neutral stimuli. While autonomic responsivity to neutral faces was associated with social functioning in all children, converging profiles characterized children with WS contrasted with TD and ASD.