Marketing of foods and beverages high in fat, sugar and salt are suggested to contribute to poor dietary behaviours in children and diet-related diseases later in life. This systematic review and meta-analysis of randomized trials aimed to assess the effects of unhealthy food and beverage marketing on dietary intake (grams or kilocalories) and dietary preference (preference score or percentage of participants who selected specific foods/beverages) among children 2 to 18 years of age. We searched MEDLINE, EMBASE and PsycINFO up to January 2015 for terms related to advertising, unhealthy foods or beverages among children. Randomized trials that assessed the effects of unhealthy food and beverage marketing compared with non-dietary advertisement or no advertisement in children were considered eligible. Two authors independently extracted information on study characteristics and outcomes of interest and assessed risk of bias and the overall quality of evidence using grade methodology. Meta-analysis was conducted separately for dietary intake and preference using a random-effects model. We identified 29 eligible studies, of which 17 studies were included for meta-analysis of dietary preference and nine for meta-analysis of dietary intake. Almost half of the studies were at high risk of bias. Our meta-analysis showed that in children exposed to unhealthy dietary marketing, dietary intake significantly increased (mean difference [MD] = 30.4 kcal, 95% confidence interval [CI] 2.9 to 57.9, and MD = 4.8 g, 95%CI 0.8 to 8.8) during or shortly after exposure to advertisements. Similarly, children exposed to the unhealthy dietary marketing had a higher risk of selecting the advertised foods or beverages (relative risk = 1.1, 95%CI 1.0 to 1.2; P = 0.052). The evidence indicates that unhealthy food and beverage marketing increases dietary intake (moderate quality evidence) and preference (moderate to low quality evidence) for energy-dense, low-nutrition food and beverage. Unhealthy food and beverage marketing increased dietary intake and influenced dietary preference in children during or shortly after exposure to advertisements. © 2016 World Obesity.