Technology can create evidence more convincing than fake reindeer tracks in the snow—though without a deft touch, Santa can come off looking like a perp in a security video. As adults seek slicker proof to back up the legends of childhood—the existence of Santa, the Tooth Fairy, the Easter Bunny—there's new confusion over the line between harmless fibs and outright deception. "I want it to be playful and fun—I don't want it to be the source of future therapy sessions," says Amy Lupold Bair, whose four-year-old, Noah, often turns to the computer to back up his parents' assertions.