Bwahahaahathisissoawesome.
It's not mentioned on Old Chum's flickr page, so I asked. [Old Chum is actually the flickr stream of Vancouver's own heritage central, Old Faithful Shop.]
And so we learn that this photo is from The Family of Children, one of the unofficial sequel/spinoffs from Edward Steichen's landmark photo exhibition and book, Family of Man.
Family of Children was produced in 1977 by Jerry Mason, who was involved in creating the Family of Man book 22 years earlier. I may have more to say on this once my copy arrives, but right now, I'll just let this awesome photo speak for itself.
Buy The Family of Children on Amazon [amazon]
I used to pour over this book when I was a kid, I should get a copy to show my kids how awesome the 70's were.