Phooey. More like it's the result of sedentary lifestyles--computers, television, video games.
Much of the TV, computers, and television is due to overworked parents using them as electronic babysitters.
I think welfare (lower class), high taxes (middle class), and feminism (upper class) have taken away the millenia old system of the mother at home, in one generation. Many, many aspects of life now suffer.
That's only part of it. Parents in this day and age have to keep a much tighter leash on their kids than they did a generation or two ago. I would be in full panic mode if my kids did a disappearing number like I used to do when I was a kid & my mom was at home full time.