Every painting app suitable for my 2 year old on the google play store was either crap, or laden with ads.. so I decided to throw something together to remedy this.
It's built in HTML5 and is my first real play with Canvas.
It should work in browser on any non-ancient touch device (though i've only test it on my Nexus 7 and iPhone 4). It (more than likely) won't work on a desktop, as i've specifically targetted touch events and not mouse events.
You can try it out at http://www.smiff.co.uk/kidpaint/
Of course, lots of features could be added, but for now it does the job it was made to do.
The included APK has been complied via the PhoneGap cloud compiler (https://build.phonegap.com/), which is bloody amazing if you can't be bothered to set up the SDK and PhoneGap.
Feel free to fork and add features, or laugh at my dodgy code :)