A lot of the problems with over weight come from eating the wrong foods. Back when mom was home all day, she had time to plan good nutritious meals. There weren't so many fast food places or so much junk food. There weren't commercials for them every fifteen minutes on tv reminding kids how good they are.
These days, so many moms have to work. After working all day, its hard to make a good dinner. It's so much easier and quicker to grab something on the way home, or make one of those mostly pre-made, pre-packaged quick meals. Those things are high in fat and calories and low in nutrition. And the amount of soda that's consumed, along with the sugar adds to the problem.