Children’s increasing use of social video platforms like YouTube and TikTok raises safety concerns for parents, yet little research explores how they mediate their children’s social video consumption. Previous studies often treat online harms and benefits as outcomes of parental mediation, overlooking how these factors affect parental mediation or how these effects vary with parents’ self-efficacy. To address these gaps, we surveyed 285 parents and found that perceived content informativeness value and content-inherent harm increase mediation, while entertainment value and creator trustworthiness decrease it. Parents’ self-efficacy—digital literacy and confidence in understanding their children’s consumption—and children’s consumption frequency significantly moderate these effects. These findings lead us to discuss how parental mediation differs between traditional media and social video platforms, where parents perform a more complex benefit-harm analysis due to competing effects of perceived harms and benefits. We propose strategies for enhancing parents’ self-efficacy and platform-parent collaboration in children’s online safety.