Background: Child obesity is considered a public health problem worldwide. According to the Pan American Health Organization (PAHO), the rates of overweight and obesity have increased disproportionately throughout the world, especially in the Americas, and with greater impact on children. Increase ranges from 11% to 21% from the year 1990 to the year 2000 in child population; in the Americas an increase is observed, with a rise of 24% in Mexico, 14% in Chile and 12% in Peru. In accord to PAHO data and the World Health Organization, this obesity is related to risk factors that are inducers which can generate obesity. Purpose: Determine the effectiveness of prescription of physical activity in overweight and obese child population according to the levels of evidence through a systematic revision in randomized controlled clinical trials in children under 16 of the physical activity programs, considering as result variables body mass index (BMI), BMI Z score and % fat. Methods: Four databases were used electronically: Pubmed, Embase, Cochrane and Lilacs. The search was conducted with a cut-off date of June 2012. Randomized controlled clinical trials of intervention programs of physical activity in overweight and obese children were selected. Two independent researchers evaluated the quality of the studies, extracted intervention and result data. Mean difference and its standard deviation were attained using the formulas suggested in the Cochrane manual Revman5.1. With this software the presence of homogeneity and heterogeneity was established. For this the statistics of I2, and Chi squared (Chi2) with its degrees of freedom and value P, were used. The magnitude of the effect of the measurement was established according to criteria suggested by Cohen in accord to size of effect. For heterogeneity of studies Galbraith graphs with EPIDATA were used to identify the heterogeneity. Results: A total of 204 studies were identified. Nineteen randomized controlled studies which complied with inclusion and exclusion criteria were included; these studies evaluated the impact of physical activity among obese children in different types of intervention based on exercise and diet or combined with the objective of reducing weight in obese children. The result variables were BMI, BMI Z score and % fat. 3 schemes of intervention were identified: (a) exercise versus no exercise, 9 studies; (b) exercise and diet versus diet, 6 studies and (c) exercise versus counseling, 3 studies. The studies included presented high heterogeneity levels of I2 of 73% Chi2 of 18.82 at 5 degrees of freedom with a value P of 0.002, which explain why they were presented in an explanatory manner. Conclusion(s): The data obtained, though they are the result of high statistical heterogeneity, clinically show the impact of overweight and obesity reduction. Implications: It is important to highlight as better intervention due to its effectiveness, the scheme of exercise and diet versus diet, which enable us to suggest that the integral program composed by structured exercise with clear prescription variables such as intensity, duration, frequency and time of specific diet prescription of hypo caloric base, facilitates weight reduction in children.