Yep, late 40s and 50s in CA same here and there were few overweight kids.
First of all, at recess we were made to go outside and do physical things. Usually without any supervision. We burned the calories we ate.
I went to school during the same time period and we'd never heard of a school cafeteria. Our Moms (mine was a single working Mom) packed our brown-bag lunches daily. I remember Sockeye salmon sandwiches (the canned was cheap then), tuna, peanut butter & jelly, always with an apple or orange for "dessert." We had fat kids and thin kids and in-between kids but in those days we realized body types differ a lot based on genetics. This whole "obesity" binge is just more meddling from Lefties who want to run everyone's lives.