I remember the first seat belts (front only) we had. Dad ordered a kit and installed them. My young self helped. I held a wrench on each nut as he tightened its bolt. somewhere in the 1962-1964 time frame, I think. That would have been a Ford station wagon, but I don't recall the model. We had a Falcon until 1960, but I don't remember what replaced it- either a Fairlane or a Galaxie. (Definitely a three on the tree, for anyone who recalls those.)
Ironically, on long trips, we'd lay eth back seats down and put a mattress in the back. All four of us kids would hang out back there, at least until we got our first air conditioner.