A preliminary study of young children undergoing treatment for cavities in their baby teeth found that nearly 28 percent had a body mass index (BMI) above the 85th percentile, indicating overweight or obesity. That percentage is more than 5 percent higher than the estimated national average, adding more fuel to the growing concern that poor food choices, including those sugary drinks and fruit juices so popular and convenient, likely are contributing to both obesity and tooth decay in very young children.