A large research literature details the powerful behavioral consequences that a trustworthy appearance can have on adult behavior. Surprisingly, few studies have investigated how these biases operate among children, despite the theoretical importance of understanding when these biases emerge in development. Here, we used an economic trust game to systematically investigate trust behavior in young children (5-8 years), older children (9-12 years) and adults. Participants played the game with child and adult ‘partners’ that varied in emotional expression (mild displays of happiness and anger, and a neutral baseline), which is known to modulate perceived trustworthiness. Strikingly, both groups of children showed adult-like facial appearance biases when trusting others, with no ‘own-age bias’. There were no developmental differences in the magnitude of this effect, which supports adult-like overgeneralisation of these transient emotion cues into enduring trait impressions that guide interpersonal behavior from as early as 5 years of age. Irrespective of whether or not they were explicitly directed to do so, all participants modulated their behavior in line with the emotion cues: more generous/trusting with happy partners, followed by neutral and then angry. These findings speak to the impressive sophistication of children’s early social cognition and provide key insights into the causal mechanisms driving trait impressions, suggesting they are not necessarily contingent upon protracted social experience.