Abstract: Social-emotional competence (SEC) is fundamental to young children's sustainable development and well-being. While parental playfulness—a positive psychological trait with intergenerational transmission properties—has been shown to promote SEC development, its underlying mechanisms remain underexplored. This study investigated how parental playfulness enhances SEC through parental emotional intimacy and emotional support, while examining the overall moderating role of family socioeconomic status (SES). Using a hybrid sampling approach (stratified proportional sampling combined with snowball sampling), we collected data from 2, 573 parents of 3-to 6-year-olds in Guangdong Province, Mainland China. Key findings revealed: (1) Direct Effect: Parental playfulness significantly predicted children's SEC. (2) Independent Mediation: Both parental emotional intimacy and emotional support independently mediated this relationship. (3) Serial Mediation: Emotional intimacy and support sequentially mediated the playfulness-SEC link, suggesting synergistic effects. (4) SES Moderation: These pathways showed significant variation across SES levels, with stronger effects in higher-SES families. These results advance theoretical understanding by: Identifying dual affective pathways (intimacy → support) in playfulness-SEC transmission; Demonstrating SES-dependent plasticity in parental influence mechanisms. Practical implications include developing play-based parenting interventions tailored to families' socioeconomic contexts.