When I was much younger my parents belonged to a "play group", where parents would take turns baby sitting each others children. Simple printed cards were "paid

When I was much younger my parents belonged to a "play group", where parents would take turns baby sitting each others children. Simple printed cards were "paid" each visit and could be redeemed upon other visits. It worked out pretty well and we kids all got to play together. One astonishing outcome: I'm still good friends with someone I met before I have any conscious memory. Kind of cool, right?