Thanks, Dave. Your information goes to confirm my suspicions (or support my prejudices, depending on how you look at it). I think one shouldn't accept scares like the obesity figures without having a look around. In this case, I don't see the obese kids in the numbers claimed. I DO see children who are far taller and fitter-looking than when I was their age, and I truly doubt how a coarse measure such as BMI can be applied to such a disparate range of shapes and sizes. I recall how my no. 1 son was above the 100th percentile(???) for height on the NHS growth charts when he was young. He's 6'5" now. He has never been the tallest in his class. His friends at school have had various growth rates, some were small until 15 or so, then shot up to over 6ft. I don't think small sample trend analysis over short periods can work here.
It amazes me continually that BMI is considered a reasonable measure of anything. What amazes me more is that reasonable people (even Jeb) will give it credance even though they should know better. Jeb has argued that "he felt better when he had a lower BMI". Although your height may vary a little over the course of your life, it is not likely to be that much. What that statement really means is "he felt better when he weighed less".
BMI is effectively Kg/m^2. This almost looks like a pressure, but has no relavance to a persons appropriate size. Density my be a useful number to use, but even that is a little iffy when it comes to people. The fact that this number is useless is becoming more clear now that kids are growing up with adequate resources. The reason childhood BMI is going up is because they do not lack for calories to feed growth. Even my parents generation (born 1944) scrounged a little for calories. We don't have to. People aren't evolving taller, they are just maximizing their potential through access to resources.
We can argue if that is a bad thing. If calories suddenly become scarce, people like me are going to be the ones in trouble. At the very least I will probably lose a lot of weight.