The biggest danger the comes from having overweight parents, is the loss of opportunity for learning good eating habits. When parents feed their kids junk, it becomes that much harder for the kids to turn themselves around later on in life.
So, given that so many parents are complete and utter failures at teaching their kids to live healthy lifestyles, it would be nice for schools to do more in the way of providing the required information, healthy food, and exercise. This goes for elementary schools, middle schools, and to some degree, high schools.
(High schools could have a vending machine or two, sure, but my school had a whole store of candy and chips. If you wanted something other than junk food, you had to buy the school's not so much up to par lunch, or bring your own. More could be done to provide some better options, and to make those better options actually seem somewhat appetizing.)