Mothers play a key role in ensuring their children’s healthy life. This study aimed to identify the maternal factors affecting problematic smartphone use in children. We adopted a cross-sectional descriptive design using structured questionnaires. Participants were fourth to sixth grade elementary school students in Korea (n = 184). The following maternal factors were evaluated: maternal mediation, children’s perception of mothers’ smartphone use, mother–child communication, and parenting style. Data regarding maternal factors’ effect on problematic smartphone use were analyzed by computing descriptive statistics and logistic regression analysis using SPSS Win 27.0. The results show that the maternal factors that influenced problematic smartphone use in children were maternal control over smartphone usage (odds ratio (OR) = 5.10, 95% confidence interval (CI): 1.33–19.60), smartphone usage time for social network service (OR = 1.52, 95% CI: 1.10–2.01), and problematic mother–child communication (OR = 1.07, 95% CI: 1.00–1.14). Therefore, to promote appropriate smartphone use among school children, it is necessary to develop an intervention comprising maternal supervision of their children’s smartphones, guidance provision for social network service usage, and strategies for the reinforcement of positive mother–child communication.