Smash Key is written in .NET and is used when you have a kid on your lap who wants to smash the keyboard. With Smash Key open, it won't wreak havoc.
It requires no installation and is portable as long as you have .NET installed (it comes with Vista and Windows 7). It's tiny because I don't include any of the sound files. It plays random audio files from your Windows system directory's media folder.
To use it, just run it and it will start in full screen mode. Hit the keyboard or click the mouse and you'll hear a sound and see a random shape drawn on the screen. I wrote this in a few hours to learn a little C# programming, so it's by no means complete or full-featured. Other similar software includes Scott Hanselman's Baby Smash and the first one I came across, BabySplat
Works on all versions of Windows, 32 and 64-bit, requires .NET 3.5 or higher.
Source available at github
Updated Jan 06, 2017