Not sure where you can get a 99 cent burger, McDonald's has the dollar menu, so maybe that's what they meant in this image? But a salad does not have to cost $4.99 if you make it yourself! Grow your own veggies or go to the store and get a head of lettuce for $1, that's enough for 4-5 salads!
Eating healthy is not as expensive as everyone thinks, it's just a matter of convenience/time. People are lazy to take the time to grow a garden or cook healthy meals. They turn to macaroni, ramen, frozen dinners and other packaged processed foods.
It has nothing do with cost, in my opinion, but everything to do with time. I love to cook, but even I have those long busy days where all I want to is pop a frozen pizza in the oven. The problem is when all people are doing is eating pizza and other junk food. We need to teach kids to eat healthy and we need parents of those kids to be willing to take the time to prepare healthy foods rather than resulting to a box of macaroni.
Next time you go shopping compare the costs of vegetables to your processed packaged foods, maybe that head of lettuce, spinach, and carrots cost more than that box of hamburger helper, but remember those veggies usually come in bulk and make more than just 1 meal unlike the box of helper. In my opinion, the costs even out, and money is just an excuse for the lazy.
Children become overweight and obese for a variety of reasons. The most common causes are genetic factors, lack of physical activity, unhealthy eating patterns, or a combination of these factors. Only in rare cases is being overweight caused by a medical condition such as a hormonal problem. (source)
So it's not just eating healthy, it can be due to not enough exercise. In today's world everyone is on their phone, their computer, or watching TV. Children play video games instead of going outside and running around.
I wanted to lose weight without changing my diet too much so I started running, already I have lost 10 pounds. I'm not willing to give up chocolate or cake, I believe in enjoying foods every now and then and pity those who won't even allow themselves a cupcake on their birthday. A slice of cake isn't going to instantly add on 5 pounds. There's a difference between having a treat every now and then versus eating cake everyday.
Anyway, there are a lot of factors and the only way to prevent obesity in my opinion is through education and good parenting. Parents need to provide healthy options for their kids and also limit screen time so they get out and get exercise. Schools also need to encourage kids to choose healthy foods and to exercise, especially since parents can't always be trusted.
Here's a great Ted Talk about the need for educating children about food: