Lucky you! Your parents must have cared. Ours was a flat slightly padded board that folded down across the back seat (eliminating the leg space) and we were allowed to bounce around on it and had to crawl on our knees to get from one side of the car to the other. (I’d forgotten that…it was great for napping on those 18 hour road trips.)
Probably wasn’t the safest idea. We did tend to wind up in a little pile against the back seat if dad hit the brakes.