Aww so sweet. I love stories like this. My wife and I met by chance in Seattle in 2014, having grown up on different coasts, but there was a period in the 1980's where we lived <50 miles apart and I always wonder whether we ever met by chance as kids. That's so amazing you found that photo. We will have to combine photo albums like you and see what we learn.
There's a reddit comment where the poster recalled, how his parents would take the family on far away cities for vacation. The parents would then do parent things and the kids would just walk around the cities. In several different cities in several different vacations, he and and his sister would run into this kid. After a few times, the kid would run being freaked out, but the poster and his sister managed to "catch" him once, and introduced him to their parents. It turns out, the poster's parents knew the kid's parents, and at vacation times, the sets of parents would travel to the same location and partner swap with each other...
> The parents would then do parent things and the kids would just walk around the cities
Apart from the final plot twist, this was surprisingly normal when I was a kid in the 1970s. The number of times my sister and I were left sitting outside a pub, either at a picnic table or even waiting in the car while the adults were inside having fun...
