Childhood obesity is defined as a medical condition characterised by abnormally high amounts of body fat relative to lean body mass, which increases the risk of adverse health outcomes among children and adolescents from birth to 18 years. The prevalence of childhood obesity, which has serious healthcare implications, is surging, together with its healthcare burden. In this review we explore the intricate interplay of hereditary, environmental, behavioural, cultural and metabolic factors contributing to the global increase in childhood obesity rates. We examine the influence of prenatal factors, genetic predispositions and epigenetic mechanisms on obesity susceptibility and treatment strategies, emphasising the importance of a multilevel life course framework to understand the multifactorial causes of obesity. This narrative review examines the epidemiology, burden, aetiology and impact of childhood obesity by focusing on published literature and the efficacy of multilevel interventions. Comprehensive algorithms are provided to illustrate the causes of childhood obesity through the lens of a multilevel life course framework, taking into consideration individual, family, community and societal factors. Genetic predispositions, including inherited tendencies towards emotional eating, metabolic variations and body fat distribution, significantly influence a child's obesity risk. Environmental factors, such as limited access to nutritious food, sedentary behaviour, insufficient opportunities for physical activity and obesogenic environments, contribute to the increasing prevalence of childhood obesity. Prenatal influences, including maternal hyperglycaemia and nutritional exposures, lead to epigenetic alterations that predispose children to obesity and metabolic disorders. The social environment, including parental influences, cultural norms and peer dynamics, shapes children's dietary habits and physical activity levels. Additionally, the review highlights the importance of early detection of metabolic alterations associated with paediatric obesity and insulin resistance and the potential for epigenetic mechanisms as therapeutic targets. Recommendations are made for tailored medical nutrition therapy, screening for syndromic obesity and multilevel interventions targeting individual and societal factors. This review underscores the necessity of a comprehensive, multilevel approach that integrates genetic, environmental, behavioural and cultural factors along with lifestyle modifications and public health initiatives to address the complex and multifaceted issue of childhood obesity effectively. Targeted interventions across the life course, policy reforms, community engagement and technological innovations are recommended to mitigate obesity risks and promote long-term health. An infographic is available for this article. INFOGRAPHIC.