You realize dinner plates these days are much much bigger than even 30 years ago? It seems that people have to eat more volume than before, to get the same amount of nutrients as before, because the food these days has more man-made chemicals and less natural goodness. And you wonder why more people today are obese and have a whole slew of other problems...
Ok, I went waaaay off topic...but then again this topic was just screaming to be taken into left field. 
i didn't actually.
i kind of tend to feel that kids are obese these days, due to lack of activity, combined with crappy food like mcdonalds, mburger king etc. i don't think it's those places themselves, as i've eaten my fair share, and am still a skinny dude.......i think it's more the lack of activity.
my understanding is that they don't even do much in this way in gym in the schools anymore, which is a big contributer to this problem.
then there's the kids going home from school, and jumping on the computer, rather than running to the field down the street, and doing things like soccer, football, etc.
i pretty much hate sports, but as a kid, we were all outside all the time. the main rule was to be in before the street lights came on. if we had to, we played softball in the street right in front of home.
it seems different today though.
now, what you mentioned about all the manmade junk in food these days.........that contributes a LOT to it too. among other things.
