Children's engagement in screen time is a complex issue. While some forms of screen time have consistently been associated with harm, others have been associated with gains, making it difficult to weigh the risks and benefits of use. In this umbrella review, we systematically collate and synthesise meta-analyses examining the effects of screen use on children and youth. We converted results onto a common metric to make comparisons simple, and where possible we reanalysed study-level data to

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... dardise the approach across meta-analyses. We identified 116 meta-analyses, and extracted 165 unique exposure/outcome combinations. These effects represent the findings of 2,171 primary studies comprised of 1,652,944 participants. When focusing on the meta-analyses with the most statistically robust evidence, we found that general screen use (when content was not indicated), was associated with potentially harmful impacts on learning, literacy, body composition, and depression. Like-wise, social media was consistently associated with risks to health, with no identified benefits. However, we also found that these harms could often be mitigated by certain kinds of content (e.g., educational), or by modifying the context (e.g., co-viewing with a parent). In summary, our findings point to the need for careful and nuanced guidelines that support parents to make the best decisions for their children.