What has changed considerably is their level of physical activity. Once they used to walk or cycle to school. Now they are chauffeured by their parents. Once they used to play in the street after school. Now they sit in front of television sets, play videos and computer games, and scan the internet.
Parents, for their part, are often equally culpable, because of their reliance on cars, their sedentary jobs and passive forms of recreation.
The Waikato research paper identifies this "obesogenic" environment. Yet rather than focusing on ways of ameliorating it - by, for example, suggesting ways of educating the public about healthy eating or ensuring children get enough exercise - it chooses to concentrate on an issue that is, at best, peripheral.
Even if fast-food sponsorship were banned, it would not make much impression on the consumption of the product.
More to the point, it is surely inarguable that the likes of McDonald's are helping children to become active and encouraging them to play sport. As such, this is, in many ways, a healthy association. McDonald's sponsors more than 300 New Zealand sports clubs and teams, as well as some high-profile children's events.
Burger King sponsors the highly successful New Zealand Breakers basketball team. How many children have been persuaded by the prominence of that team to switch off computer games and pick up a basketball?
And what might replace fast-food sponsorship if it was outlawed?
People know what and how much they and their children should be eating and that they and their children should be exercising regularly. One in 12 New Zealand children is obese, so there is clearly a problem, not least in the future burden on the public health purse.
But stopping fast-food chains' sponsorship of charities and sports events would be no solution. Public health lobbyists might feel a righteous sense of accomplishment. But they will have done nothing to address the public behaviour that lies at the root of the problem.