I sympathize with anyone who can't afford to provide proper nutrition for his or her children due to poverty or food deserts. However, is it generally true that "the only food they can afford are nutritionally null processed foods"? At my grocery store I buy fresh fruit that's already washed, peeled, cut, and ready to eat. The cost is $6 per pound, which is less than a Big Mac with fries.

If I walk into McDonald's and see an obese mom buying her obese son a combo meal, my first thought isn't "she can't afford to provide proper nutrition for him," but rather "perhaps she doesn't know better or perhaps her son refuses to eat nutritious food." If the mom were offered fresh fruit and vegetables instead of the burger, would she and her son accept the healthier choice?

In many (most?) cases in the US today, it's not as simple as "healthy food is too expensive for poor people." Perhaps once we can create food using a nanofactory, we can make spinach and broccoli that tastes like a cheeseburger and French fries. Till then we will have the problem of trying to convince people to eat what's good for them.