Excessive use of smartphones and tablets has become increasingly common among children, contributing to adverse physical and mental health outcomes. Evening chronotype and inadequate sleep habits have been identified as potential risk factors. However, despite growing concerns, there is limited evidence on the relationship between chronotype, sleep patterns, and digital device addiction in children. In this cross-sectional study, 213 Iranian schoolchildren aged 4-11 years were assessed using validated Persian versions of three standardized instruments: the Children's Chronotype Questionnaire (CCTQ), the Children's Sleep Habits Questionnaire (CSHQ), and the Smartphone and Tablet Addiction Questionnaire. This is the first study in Iran to employ the CCTQ to examine the association between chronotype and smartphone addiction in children. Data analysis included descriptive statistics, Spearman's correlation, stepwise regression, and Kruskal-Wallis tests. Sleep problems and smartphone/tablet addiction were significantly more prevalent in children with an evening chronotype, followed by those with a neutral chronotype, and were lowest in those with a morning chronotype. In addition, the M/E and CSHQ scores were positively associated with smartphone/tablet addiction scores, whereas later sleep onset time on scheduled days showed a negative association. Specifically, each one-unit increase in the M/E score was linked to a 0.75-point increase in the average addiction score (β = 0.75, SE = 0.17, < 0.01), and each one-unit increase in the CSHQ score corresponded to a 0.35-point increase (β = 0.35, SE = 0.13, < 0.05). Conversely, each one-unit delay in sleep onset time on scheduled days was associated with a 0.15-point decrease in the average addiction score (β = -0.15, SE = 0.09, < 0.05). Children with an evening chronotype appear more susceptible to both poor sleep habits and smartphone/tablet addiction. These findings, in line with previous research on adolescents and adults, support the notion that circadian misalignment plays a pivotal role in technology-related behavioral risks. Early identification of chronotype and the implementation of strategies to promote healthier sleep schedules may be beneficial for fostering healthier sleep patterns and more balanced device use among children. p p p
