Thirteen RCTs were included in the review (3,133 participants, range 21 to 1,295), five of which were cluster RCTs. Sequence generation was adequate in nine trials. Allocation concealment was adequate in six trials. Blinding was not reported in most trials. Where reported, more than 20% of trial participants were lost to follow-up (two trials). Two of the five cluster RCTs reported adequate recruitment methods. Based on the GRADE score, outcomes of BMI and screen time viewing were judged as low quality evidence.
There was no significant reduction in BMI in the intervention group compared with the control group (WMD -0.10, 95% CI −0.28 to 0.09; six RCTs). No significant difference was found in the amount of screen time as measured by reported hours per week between the two groups (WMD -0.90 hours/week, 95% CI -3.47 to 1.66; nine RCTs). Significant heterogeneity was observed only in the outcome of the amount of screen time (Ι²=66%).
Subgroup analysis of preschool children (younger than six years) showed a significant reduction in screen time in the intervention group compared with the control group (WMD -3.72 hours/week, 95% CI -7.23 to -0.20; two RCTs). No significant heterogeneity was observed in this outcome.