Summary Children are increasingly exposed to food and beverage marketing, but little is known about the specific effects of marketing through media most used by children. This study aims to systematically review the influence of unhealthy food and beverage marketing through social media and advergaming on diet‐related outcomes in children. Seven databases were systematically searched for English peer‐reviewed quantitative and qualitative scientific studies on the effects of marketing of unhealthy products through social media or advergaming on a range of diet‐related outcomes in children. Risk of bias was assessed with tools specific for the different study designs. Twenty‐six studies were included, of which 20 examined the effect of food and beverage marketing through advergaming and six through social media. Most studies had a high risk of bias. The results suggested that unhealthy food and beverage marketing through social media and advergaming has a significant effect on pester behaviors, food choice, and food intake of children. The studies demonstrate that unhealthy food and beverage marketing through media popular with children significantly impacts different diet‐related outcomes. Combined with existing evidence on this effect in other settings, this review provides clear evidence of the need for policies targeting screen‐based marketing.