Obesity is a growing problem in developed countries and is likely a major cause of the increased prevalence of high blood pressure in children. The aim of this review is to provide clinicians and clinical scientists with an overview of the current state of the literature describing the negative influence of obesity on blood pressure and it’s determinants in children. In short, we discuss the array of vascular abnormalities seen in overweight children and adolescents, including endothelial dysfunction, arterial stiffening and insulin resistance. We also discuss the potential role of an increased activation of the sympathetic nervous system in the development of high blood pressure and vascular dysfunction associated with obesity. As there is little consensus regarding the methods to prevent or treat high blood pressure in children, we also provide a summary of the evidence supporting relationship between physical activity and blood pressure in children and adolescents. After reviewing a number of physical activity intervention studies performed in children, it appears as though 40 minutes of moderate to vigorous aerobic-based physical activity 3–5 days/week is required to improve vascular function and reduce blood pressure in obese children. Future studies should focus on describing the influence of physical activity on blood pressure control in overweight children.