Objectives: The prevalence of smartphone use among children raises concerns about the potential for problematic smartphone use. According to previous findings, it was reported that psychological factors affect children’s problematic smartphone use. However, cognitive factors affecting children’s problematic smartphone use have not been investigated enough. To find out how to mitigate and prevent their problematic smartphone use, the present study explores whether children’s negative automatic thoughts affect their problematic smartphone use. It also seeks to investigate the moderation effect of weekend family rituals on the relationship between children’s negative automatic thoughts and problematic smartphone use.Methods: The study participants included 274 fifth and sixth graders attending elementary schools in Seoul and Incheon, South Korea. Statistical analysis for the present study was conducted using SPSS 22.0 and PROCESS macro version 3.2.Results: The study found that children’s negative automatic thoughts are positively related to problematic smartphone use. In addition, children’s negative automatic thoughts are adversely related to weekend rituals, and weekends ritual are also negatively associated with children’s problematic smartphone use. Children’s negative automatic thoughts have an effect on their problematic smartphone use. It also found that weekend family rituals moderated the association between children’s negative automatic thoughts and their problematic smartphone use. That is, children who automatically perceive themselves negatively tend to be dependent on smartphones.Conclusion: Based on the results, this study suggests that it is necessary not only to design intervention programs for preventing children’s problematic smartphone use but also to support work and life balance so that families can create and maintain their weekend family rituals.