(1) Background: Abdominal obesity describes the accumulation of visceral fat. Monitoring of abdominal obesity in children aids prognosis of atherogenic risk and prediction of the emergence of different comorbidities, many of which persist into and throughout adulthood. For this reason, it is of great diagnostic value to the sustainability of health in populations. The aim of this study was to evaluate abdominal obesity in overweight schoolchildren from Portoviejo (Ecuador) and propose conicity index cut-points for sustainable health. (2) Methods: The sample was formed by 356 schoolchildren whose BMI z-score deemed them to be overweight. Height, weight, waist circumference (wstC), various skinfolds, percent body fat, conicity index (CI) and overweight classification according to wstC were determined. (3) Results: The mean age was 6.83 ± 1.2 years, 17.4% were obese, 34.8% were overweight and 47.8% were at risk of being overweight according to their BMI z-score. The mean height was 1.29 ± 0.12 m, whilst the mean weight was 35.21 ± 11.57 kg. When classifying according to wstC, 37.9% were identified as obese, 28.1% had high-risk abdominal adiposity and 34% were normal. The average CI was 1.16 ± 0.06, whilst that of body fat was 19.34 ± 6.03, with 56.2% of individuals having body fat values lower than 20%. (4) Conclusions: The sample showed a high prevalence of central obesity. Significant agreement was not found between classifications of nutritional status according to BMI z-score and wstC.