Cameron, my little cousin (he's eight) and I have made simple 2d arcade games with Stagecast Creator. We did one when he was five: a Godzilla battling game. I did the programming; he did the artwork. Recently, he went through a couple Stagecast tutorials by himself. Afterwards, we created a game where we shared in the programming and the artwork. It's fun to see him program, even though he can't articulate what a variable or loop is; Stagecast has a visual programming language that uses no words.
We also made a stop-motion animation movie with Stop Motion Pro called "The Ambush", with his dinosaur action figures...yes, he likes dinosaurs.
Cameron and I designed a 3d model of a church using SketchUp. Thanks to Buckley for the introduction to SketchUp.
Cameron likes to "photoshop" himself into movie posters using Paint.NET.
Except for Paint.NET, these applications are available on Mac and Windows. Paint.NET and SketchUp are free. Stagecast and Stop Motion Pro both have free trials.