From Academic Kids
The slide whistle is most commonly used as a sound effect (such as in the sound tracks of animated cartoons, when a glissando can suggest something rapidly ascending or falling), but it is also possible to play melodies on the slide whistle.
The instrument became common in the 1920s when it was occasionally used in popular music and jazz as a special effect. Louis Armstrong switched over from his more usual cornet to the slide whistle for a chorus on a couple of recordings with King Oliver's band and his own Hot 5. At that time, slide saxophones, with reeds rather than a fipple, were also built.
The slide whistle is today thought of primarily as a kind of "toy" instrument, but has been used by classical composers, with Maurice Ravel possibly being the first, when he called for one in his ballet, L'enfant et les sortil觥s. More modern uses in classical music include Luciano Berio's Passaggio, which uses five, and pieces by Cornelius Cardew, Alberto Ginastera and Hans Werner Henze.
To fans of 1970s BBC children's television, the instrument will always be associated with the voices of the Clangers. The instrument also features prominently in the game of "Swanee-Kazoo" in the long-running British radio panel game, I'm Sorry I Haven't A Clue.