The tale behind a new museum of children’s literature is equal parts imagination, chutzpah and “The Little Engine That Could.” On a crisp Saturday morning that screamed for adventure, a former tin can factory in North Kansas City, Mo., thrummed with the sound of young people climbing, sliding, spinning, jumping, exploring and reading. Yes, reading. Welcome to the Rabbit Hole, a brand-new, decade-in-the-making museum of children’s literature founded by the only people with the stamina for such a feat: former bookstore owners.