What is the greatest barrier to obesity prevention?

Obesity prevention obviously starts with children. Adults who are not over weight probably already have their weight at least somewhat figured out.
Children spend most of their time at school or at home.
At school there is very little opportunity for exercise. Many middle schools don’t have any kind of recess, the PE classes are lame and focus on the few athletic kids and the mass-production environment makes it difficult for the less athletic kids to come out and get active. Kids get hungry and there are few healthy options that aren’t disgusting. The halls are packed with vending machines and a coke is cheaper than a box of orange juice.
Then the kids go home and they have two hours of homework. When they’re done there isn’t much a kid can do if they’re not involved in sports except facebook, watch TV and play video games. Kids don’t have much control over what food is in their houses so they often resort to packaged snack food until, if they’re lucky, their parents come home and make them one half-way healthy meal for the day.
All this comes down to the basics: Poor diet and lack of exercise. Parents and schools need to see to it that kids have easy access to both. With 47% percent of Americans dying every year of heart disease related to poor diet and lack of exercise this is really an important issue.