Nothing could be sweeter than the sound of children singing — until you throw their angelic voices into a minor key, add some spooky sound effects, and use it to score a movie trailer. The new Avengers: Age of Ultron trailer, for example, plays the song “I’ve Got No Strings” from Disney’s Pinocchio to shudder-inducing effect. Such twisted children’s songs are a staple of classic horror films like A Nightmare on Elm Street, which adapted its haunting “One, two, Freddy’s coming for you” chant from the English nursery rhyme “One, Two, Buckle My Shoe." But creepy covers sung by kids pack their biggest emotional punch in trailers. The boy soprano singing "The Star-Spangled Banner" in the Dark Knight Rises trailer underlines the film’s crushing bleakness, and that off-key rendition of "Roses are Red" in the Suspiria trailer telegraphs the macabre humor of Dario Argento’s cult favorite. Watch our ultimate mix-tape of classic songs getting a creepy makeovers in Yahoo’s movie-trailer compilation above.