Adults with obesity have an imbalance of bacteria in their intestines which may contribute to weight gain and diseases related to obesity. Restoring the balance of these bacteria (the "microbiota") could help reduce weight and related diseases. However, little is known about this imbalance in children with obesity. This research study will map out the compositions of the gut microbiota of children and compare them with those of children who have healthy weights and different degrees of obesity. This project will also measure the amounts of fatty acids in the stools which are an indication of how efficiently the intestines absorb calories from food. If an imbalance is detected in children with obesity, then this information can help researchers test ways to restore the gut microbiota with hopes of reducing weight and some of its related health problems.