If you've done quite a bit of research and know pretty much what you want to say, then you just need to come up with a statement that summarizes it all. But first, you want to make sure that you don't have any ideas that don't belong, or don't fit. Looking at what you have above, I'm wondering if the idea of food addiction belongs with the rest of your ideas. I'm not sure that is something that fits with parents taking responsibility, McDonald's, etc. I could be wrong.
That said, it sounds to me like your final statement might serve as your thesis. If you go with the fact that parents need to start monitoring, managing, whatever, what their kids eat, I think everything else could be used as evidence to support that.
Of course, you probably want to be more specific than that parents should take responsibility. You want to be able to write exactly what parents should do. Taking responsibility is vague. What exactly do parents need to do? What concrete steps can parents take? I suggest you come up with exactly what parents should do, and go with that for your thesis.