Novel-length. Thing is, the rest of the story takes place on Long Island in 1950, with only scattered clues that one of the adult characters might be one of the little girls from the prologue. I like stories where the reader is allowed to collect the dots, so that’s how I usually try to write, but it’s tricky to judge, when you’re the one planting the information , whether you’re being annoyingly obvious or bafflingly obscure.