Anything like the old MacPaint for OS X?

I recently switched my nephew from Windows to a Mac. He loves to use Paint in Windows, and unfortunately there is no alternative in OS X that I can find. I have apps like Photoshop and Illustrator, but he prefers the very simple interface of Paint, which is essentially the same as MacPaint. Can someone point me in the direction of an app that won't require too much of a learning curve for him, and is free?

Thanks