Flavored milk provides the same nine essential nutrients as unflavored milk, including three of the five nutrients identified as "nutrients of concern" for children in the 2005 Dietary Guidelines for Americans - calcium, magnesium and potassium. Milk is the number one source of calcium, magnesium, potassium and phosphorus in children's diets.
The sugar content of flavored milk has been alleged to contribute to obesity. However, a study in the Journal of the American Dietetic Association found that when people choose chocolate milk over sugary juice and soda they got more protein, vitamins and calcium in their diet without increasing total added sugar or fat.
So go ahead treat yourself RIGHT, have a glass or two of chocolate milk. And if it helps any, keep the healthy stuff a secret.
(Journal of the American Medical Association)