Is it really the fat in food that is making us fat and causing so many health problems?

I remember my mother cooking all our meals with real fat. Many of our meats where fried in cooking fat and tasted great. We drank whole milk, and ate cereal with sugars, and did we love our bread.
We also ate a lot of carbs, rice, pasta, and there was a lot of seasoning in our food as well. We never missed a meal. And a glass of hot chocolate and cheese and crackers after school for a snack or a jelly sandwich. Yes, we ate salads and fruits but not as much as the stuff mentioned. All of my friends moms also cooked in about the same fashion. None of us were obese. What we considered fat then was maybe a kid about 20 lbs. In grade school we only had one kid who was fat and he had a heart problem and all his siblings were thin. Even the adults weren’t ever really fat.
As for the health issues. Now babies are developing acid reflux. Kids are weighing over 100 lbs their weight. Adults are weighing 300 lbs.
I know there are a lot of things going into that, like fast foods. But why would fast food grease be worse than what we ate as children?
Salt is almost completely being erased from the menu in restuarants. So why are we so much heavier. By the way, we also ate a lot of candy, icecream and cupcakes, and chips, and we still were normal weight. So why the change?