The icing may seem thick at first, but don't be tempted to thin it. It will flow just enough to drip slightly down the side of each doughnut. If it's too thin, it won't set up and will run off the doughnut.
Try coloring the icing red, white and blue for a patriotic theme or the colors of your favorite sports team. Experiment with different patterns: spoon one color over the top, then add drops of another color. Watch the pattern it makes as the icing spreads. Kids will love to experiment with this.
Immediately after icing the doughnuts, sprinkle with colored sugar or edible glitter.