Focusing on kids, because that's where I've got the clearest reference for making my own comparisons: 30 years ago, kids in my neighborhood spent most their time running around outdoors. I'm not even sure everyone's parents knew where they were half the time, and it was fine as long as you made it home for dinner. Nowadays, kids seem to spend most their time playing Minecraft or Fortnite or whatever. I don't see them often on the sidewalk unless they're headed to or from school, and the playgrounds are generally pretty quiet. Over the same time period, hours of TV watched per household is up by about 2 hours per day, and consumption of the Internet has gone from zero to whatever it is right now, so that's where I'm guessing all the kids have gone.
Definitely watched a lot of Nickelodeon and Cartoon Network too.
I really wouldn't point to modern video games as the blame, look more toward how the food has changed.
Anetdotal, but the majority of people I know eat like shit.
A poor diet over a year or two will do it without trying.
We can see this clearly in China. The older generation seems to have some resistance to junk food in terms of weight gain: this is why asians have a reputation for remaining slim, even if they eat junk food. But, it's not due to their genes: they were simply lucky enough to not be introduced to those bad foods until their adulthood.
If you look at the newest generation in China in the cities, their obesity rate is skyrocketing at an extremely high rate.
How so? Growing children can probably handle a lot more junk food and sugar without any consequences than adults.
I know some people who just hate exercise. I think they has no habit of movement of any sort. Likewise, people who were fat or weak as a child have no baseline sense of what it feels to be healthy - and neither do their bodies cells.
So kids can handle more sugar, but if messed up the consequences are worse.