Chalk is one of a small but growing group of stories set in the neighbourhood where I grew up. The first one was a piece called "Eenie Meenie Ipsateenie" written for Charlie Grant's anthology series Shadows. But I didn't get around to doing another for over twenty years, when I wrote "Jimmy" for Ellen Datlow's The Del Rey Book Of Science Fiction and Fantasy.
I had always had it in the back of my mind to use my old neighbourhood in Massachusetts as a setting, but only in period, as I had known it when I was growing up (it's completely unrecognisable now). When you're a little kid, the world–i.e., what small part of it accessible to you–is simultaneously full of exciting possibilities and dangerously unpredictable. Even when you're too old to believe in Santa Claus, there are days when you can feel something in the air and magic is so close, you'd swear you could touch it if you only knew how to do it right and not scare it off...
My best friend Rosemarie and I really did draw fantastical maps on the road behind the tenement where I lived, but in regular old coloured chalk, not carpenter's chalk (the one time I had any, it was quite crumbly and made a terrible mess, and upset my mother, although she did not react like the mother in the story). Other than that, there is no resemblance–Rose and I didn't go to the same school, her family was not like the family in the story, and neither of us ever went missing (although there was an incident involving a school project where both our mothers briefly thought we had been kidnapped by the Civil Defence Department, but that's another story).
However, children did occasionally go missing. In the early 1960s US, when radio and TV were mass media, the Beatles had the longest hair anyone had ever seen on any man who wasn't Jesus, and sex education was still illegal in our state, we had no idea what could happen. (I know, that must seem so improbable here in the information-rich present; you'll just have to trust me on this.) When you don't know what to be afraid of, you use your imagination.
Rose and I had many wish-fulfilment fantasies good for hours and hours of play and one of them had to do with finding some hitherto unknown place in a neighbourhood we could have travelled through blindfolded, a spot we could have all to ourselves so secret that grown-ups couldn't see us even if they were looking directly at us. Because that did happen, in a way–there were times when grown-ups behaved as if they really didn't see us, couldn't see us. However, it occurred randomly, there was no rhyme or reason to it from our perspective. If we'd been able to figure out how it worked, we'd have had it made.
But even if we had, we were pretty sure we wouldn't have gotten away with it for very long. Grown-ups owned the world and everything in it. If there was any magic, they owned that, too, and any kids who dared to mess with their stuff would find themselves in big trouble...