This study aimed to examine the longitudinal relationship between smartphone dependency and happiness among Korean children from fourth grade in elementary school through the first year of middle school (approximately ages 9–13), thereby providing an in-depth understanding of children’s emotional development in the digital environment. Longitudinal data from four waves (2018–2021) of the Korean Children and Youth Panel Survey (KCYPS), comprising a nationally representative cohort of fourth-grade students (N = 1,889), were analyzed. Descriptive statistics, repeated measures analysis of variance, correlation analysis, and latent growth modeling (LGM) were employed. Descriptive analyses indicated a gradual decline in children’s happiness over time, whereas smartphone dependency showed a modest increasing trend. However, latent growth modeling revealed that the slope of smartphone dependency was not statistically significant, and therefore a no-change model was adopted for this construct. Across all waves, smartphone dependency was consistently and negatively correlated with happiness. Furthermore, LGM results demonstrated that higher levels of smartphone dependency were associated with less favorable trajectories of children’s happiness over time. These findings underscore the importance of adopting a longitudinal and model-based perspective to clarify the relationship between smartphone use and children’s emotional well-being, and they offer empirical implications for educational and policy interventions aimed at supporting healthy development in the digital era.
Kim et al. (2026) studied this question.