If you don't have a paper shredder, and you have a large amount of documents that you have just culled from your files and need to shred before discarding, try giving them to your 4-year-old, along with a pair of scissors, and telling your 2-year-old that she may tear them to ribbons if she would like to join the fun.
The result is a floor covered in itty bitty pieces of paper, in squares, triangles, circles, etc. several little "notes" on your desk from your son, and two or three hours of quiet while they are vastly entertained by this new enterprise.
They even helped put it all in the trash when it was done.
Operation Shredder accomplished.