Importance: Screen time has become an integral part of children's daily lives. Nevertheless, the developmental consequences of screen exposure in young children remain unclear.
Objective: To investigate the screen time trajectory from 6 to 72 months of age and its association with children's development at age 72 months in a prospective birth cohort.
Design, setting, and participants: Women in Shanghai, China, who were at 34 to 36 gestational weeks and had an expected delivery date between May 2012 and July 2013 were recruited for this cohort study. Their children were followed up at 6, 9, 12, 18, 24, 36, 48, and 72 months of age. Children's screen time was classified into 3 groups at age 6 months: continued low (ie, stable amount of screen time), late increasing (ie, sharp increase in screen time at age 36 months), and early increasing (ie, large amount of screen time in early stages that remained stable after age 36 months). Cognitive development was assessed by specially trained research staff in a research clinic. Of 262 eligible mother-offspring pairs, 152 dyads had complete data regarding all variables of interest and were included in the analyses. Data were analyzed from September 2019 to November 2021.
Exposures: Mothers reported screen times of children at 6, 9, 12, 18, 24, 36, 48, and 72 months of age.
Main outcomes and measures: The cognitive development of children was evaluated using the Wechsler Intelligence Scale for Children, 4th edition, at age 72 months. Social-emotional development was measured by the Strengths and Difficulties Questionnaire, which was completed by the child's mother. The study described demographic characteristics, maternal mental health, child's temperament at age 6 months, and mental development at age 12 months by subgroups clustered by a group-based trajectory model. Group difference was examined by analysis of variance.
Results: A total of 152 mother-offspring dyads were included in this study, including 77 girls (50.7%) and 75 boys (49.3%) (mean [SD] age of the mothers was 29.7 [3.3] years). Children's screen time trajectory from age 6 to 72 months was classified into 3 groups: continued low (110 [72.4%]), late increasing (17 [11.2%]), and early increasing (25 [16.4%]). Compared with the continued low group, the late increasing group had lower scores on the Full-Scale Intelligence Quotient (β coefficient, -8.23; 95% CI, -15.16 to -1.30; P < .05) and the General Ability Index (β coefficient, -6.42; 95% CI, -13.70 to 0.86; P = .08); the early increasing group presented with lower scores on the Full-Scale Intelligence Quotient (β coefficient, -6.68; 95% CI, -12.35 to -1.02; P < .05) and the Cognitive Proficiency Index (β coefficient, -10.56; 95% CI, -17.23 to -3.90; P < .01) and a higher total difficulties score (β coefficient, 2.62; 95% CI, 0.49-4.76; P < .05).
Conclusions and relevance: This cohort study found that excessive screen time in early years was associated with poor cognitive and social-emotional development. This finding may be helpful in encouraging awareness among parents of the importance of onset and duration of children's screen time.