Relationship of Emotional Functioning in 10–13-Year-Old Schoolchildren with Key Lifestyle Sleep Problems and Daily Physical Activity

Background/Objectives: Sleep problems and physical activity are key lifestyle behaviors associated with children’s socioemotional development. However, their relative contribution to emotional regulation and emotional instability during middle childhood remains insufficiently clarified. This study aimed to examine the associations between sleep problems, habitual physical activity, and emotional regulation in elementary school children, while controlling for sociodemographic and lifestyle confounding variables. Methods: A cross-sectional study was conducted with 386 elementary school children (mean age = 11.15 ± 0.66 years; 45.6% boys) from southern Spain. Emotional regulation was assessed using the Emotion Regulation Checklist (ERC), sleep problems were measured with the Children’s Sleep Habits Questionnaire (CSHQ), and habitual physical activity was evaluated using the Physical Activity Questionnaire for Children (PAQ-C). Age, sex, socioeconomic status, and daily screen time were included as covariates. Pearson correlations and multiple linear regression analyses were performed. Results: Sleep problems were strongly associated with lower adaptive emotional regulation and higher emotional lability. In adjusted regression models, sleep problems emerged as the most robust independent predictor of both emotional regulation and lability. Although habitual physical activity was significantly associated with emotional outcomes at the bivariate level, its predictive strength decreased after adjustment for covariates and did not independently predict adaptive emotional regulation. Conclusions: Sleep problems appear to play a central role in children’s emotional functioning during middle childhood. Interventions aimed at promoting socioemotional well-being may benefit from prioritizing sleep health alongside physical activity within a comprehensive 24 h movement behavior framework.