This state-of-the-art review on ultra-processed foods (UPF) and children consolidates evidence from around the world on how rising UPF consumption undermines children’s nutrition, health and well-being. The review finds strong evidence that UPF intake in children is linked with poor diet quality, overweight and obesity, and dental caries. A growing body of research also associates UPF intake in children with undernutrition, micronutrient deficiencies, mental health concerns, metabolic changes and an increased risk of chronic diseases later in life. This evidence provides the basis for advocating for and developing stronger legal measures and policies to counter the rise of UPFs in children's diets through actions that protect children’s food environments and place child rights before commercial interests.