While adaptive perfectionism ensures good overall performance, maladaptive perfectionism is associated with emotional disorders for which psychological treatment is sought. There are many factors that can explain the development of this disorder throughout childhood. The present study analyzed to what extent the child's personality traits and excessive parental demands can predict maladaptive perfectionism, and, in turn, also analyzed how this relates to positive emotions and depressive symptoms in a sample of 404 Argentinian children (M age = 10.30; SD = 1.03). Stepwise multiple regression analyses and Kruskal-Wallis and Mann-Whitney tests were performed. Results showed that excessive parental demands, together with high child neuroticism increased the likelihood of developing perfectionism (p < .001) throughout childhood. It was also noted that child perfectionism increased the symptoms of depression (p < .001), decreased feelings of gratitude (p = .018), increased the recognition of self-worth (p = .009) and activated certain aspects of sympathy towards others' pain (p = .043). These processes linked to perfectionism are discussed, clarifying their effects on children's mental health.