Problematic smartphone use—a pattern of excessive and dysregulated use that interferes with daily functioning (Billieux, 2012)—among children and adolescents has garnered growing attention due to its links to various psychological, emotional, and physical health challenges (Cilligol Karabey et al., 2024, Nambirajan et al., 2025). Understanding what drives this maladaptive tendency is, therefore, crucial for both theory and practice. One particularly salient factor is parental PSU, with mounting evidence suggesting that higher levels of PSU among parents are linked to similar patterns in their children (e.g., Cho & Lee, 2017; Doo and Kim, 2022, Gong et al., 2022, Lim and Jeong, 2022). However, existing findings are predominantly derived from cross-sectional data, which preclude conclusions about the directionality of this association. One longitudinal study using latent growth modeling found a positive association between changes in parental and child PSU over three years (Jeong et al., 2024), but it did not clarify the temporal precedence of these changes.

Together, it remains unclear whether parental PSU leads to subsequent PSU in children, vice versa, or bidirectional. Grounded in broader theories of parent–child mutual influence (Paschall & Mastergeorge, 2016), we expect that PSU develops through bidirectional, recursive influences between parents and children. Children may internalize and model their parents’ problematic smartphone use through observational learning (Bandura, 1977), while parents may, in turn, adjust their own usage patterns in response to their children’s behaviors, reflecting child-driven effects in the socialization process (Bell, 1968). Importantly, these reciprocal dynamics may unfold not only between families but also within them (Curran & Bauer, 2011), such that short-term fluctuations in one family member’s PSU can shape subsequent changes in the other. To test this idea, the present study examines the reciprocal link between parental and child PSU over time, using a nationally representative sample of Korean parent–child dyads who reported their PSU annually as part of the Korean Children and Youth Panel Survey (KCYPS 2018).