If you've been at all paying attention, you know that one of the big "issues" that the media has been hammering away at recently is "childhood obesity." In general, I think that our collective tendency to insist that someone be blamed for any social ill or specific harm, especially when such ills or harms befall children, is ridiculous. However, in this case, I've decided to engage in the blame game. I'm going to briefly explain the basics of how changes in weight (in particular, the retention and burning of fat) work, and I'll bet that, by the time I'm done, we'll be able to make a determination of who's to blame for the childhood obesity phenomenon.
Our bodies require energy for everything they do, from climbing mountains to fleeing from wild animals to breathing and blood circulation. All of this energy is derived from the food we eat. The energy in the food that we consume, and that is used by our bodies, is measured in units called calories (or, more precisely, kilocalories). Every day, our bodies "burn" a certain number of calories, and, in order to maintain a balance, we must consume the same number of calories (contained in the food we eat) that we burn.
If we consume the same number of calories that we burn, our weight will remain constant. Otherwise, our weight will change. If we take in more calories than we burn, our bodies have excess energy floating around. This energy is transformed by our cells into fat, to be stored until such time as its energy is needed. As fat increases, so does weight. If we consume fewer calories than our bodies need, then we burn some of our fat, transforming it back into the raw energy that the body can use. As fat is burned, weight decreases.
The ideal situation, of course, is to maintain a balance (eat the same number of calories that we burn) at the proper weight. In order to do this, we have to know how much to eat. The body uses hunger to accomplish this. Whenever our bodies need more calories, a signal is sent to our brains telling us to eat. Once we've eaten enough, another signal is sent telling us to stop eating. For some people, these signals malfunction to some degree, and that can be a cause of their weight problem. However, for most of us, as long as we consistently follow the signals our bodies send us (eat when we're hungry and stop eating when we're no longer hungry), we will maintain a basically constant weight.
Very few of us do this, though. Our eating schedules are rarely determined by the presence or absence of hunger. We eat because it's 6:00 P.M., and that's dinnertime. We eat because we're going out to lunch with a friend, and it would be awkward to sit there and not eat. We eat because someone went to the trouble to cook Thanksgiving dinner, or just a Sunday brunch, and it would be rude to not partake, and besides that food looks really good, especially dessert. There are other reasons that some people eat (depression or frustration, for example), but, in general, we eat because social circumstances dictate that we eat.
This is why a lot of people have a weight problem. But here we come to my point. Adults generally have a choice regarding when they eat, what they eat, and how much they eat. They could refuse to eat if they're not hungry when someone offers to take them out to dinner. They could decline to partake of the holiday dinner if their bodies aren't sending them that signal that says, "Feed me!" But children, especially young children, generally don't have this option. They don't get to decide when they eat; their parents do. They don't get to decide how much they eat; their parents do. Their parents insist that they come to the table at mealtime. They insist that the children eat, even if they're not particularly hungry. They insist that the children "finish your plate!" even if they throw a fit because they don't want it. It's the parents who determine portion size, and it's the children who are forced, with the threat of punishment if they don't comply, to eat it all. Since adults are accustomed to eating more than children, they typically load the child's plate with more food than the child would normally eat in a meal.
When the child is full, his body is sending a message to his brain saying, "No more food for me, thanks; I've had enough." But his parents insist that he stuff his face with the rest of his food, despite the fact that he doesn't want it (and his body doesn't need it), or he'll face a grounding (or, God forbid, a spanking). So, because he doesn't want to be punished, he eats the rest of his food. Since his body didn't need all that energy, it turns some of those calories into fat. If this scenario is repeated often enough (and it is) the child will gain weight noticeably.
This, of course, is not the sole cause of childhood obesity, but a great deal of fat children would not be fat if their parents didn't insist that they eat when they don't want to.
Here's the solution: let children eat when and how much they want. This doesn't mean to always let them eat what they want; a balanced diet is important for other reasons. But if your child is hungry, let him eat. If your child is full, don't make him eat. And for God's sake let him go outside, run around, and play. Chances are, he won't become fat like so many other children of douchebag parents will.
Conclusion: The childhood obesity phenomenon is caused in large part by ageist, dumbfuck parents who think it's their right to control what, when, and how much their children eat because children don't "know better." Children, like adults, have a perfectly good feedback system (hunger) to tell them when to eat. Let them use it, leave them the fuck alone, and save them from a childhood and possibly a lifetime of obesity.