I'm not sure they want you to believe it's "healthy" if you're using your definition of healthy. Healthy is one of those words that needs context. If you're on the cast of Survivor, it would be damn healthy. If you're comparing it to another menu item with a similar calorie content, the oatmeal might be a better choice if it helps with satiety or fills a nutritional gap in the consumer's diet. If you're comparing it to organic rolled oats boiled in water with nothing else added, it's going to look calorie laden and decadent.
But it's still the same issue. The kiddies like the taste of Coke and fries, just like I do. That isn't McD's fault, though. Don't I make the same decision when I go grocery shopping and choose between skim and whole milk...or choose to eat out instead of cooking at home?
Is it easy? Not always. But at some point I have to realize that I don't need McD's to fight my battles for me when it comes to my or my kids' food choices. I don't want or need someone protecting me from myself nor do I need McD's to help me choose what I feed my kids.
It just starts to smack a bit of "I'm smarter than those people and they need me to tell them what they can and can't do." <---Not directed at you, personally, but more the big brother notion of invasive consumer protection.