I think the earliest memory I have which is vivid and detailed ie. not a memory created around old photos and family narratives, is of falling out of the backseat of a moving car when I was about 4. P reg (1975) Ford Cortina, bright orange bodywork, chocolate brown roof.. oh yeah, very tasty. Of course, no seat belts or child locks, round a corner, door opens and I tumble out, roll over a couple of times and slide to a halt on a grass verge.
Did it hurt? Well, it never actually happened. Sure, the car was real, as was the corner, grass verge etc. I'd probably been around that corner hundreds of times in that car.. with emphasis on 'IN that car'. Yet that is still my most vivid childhood memory - a construct with only a partial basis in objective reality. happy days
but hey, saunter along the paths of cognition and you start to see that that is pretty much what memory is anyway.