I'd also recommend Ruby and suggest you take a look at Shoes (http://shoooes.net/) which makes it very easy to code GUI-apps with all sorts of fun-stuff in them like animations, downloading data from the web, videos.
The most important part in teaching a 13 year old programming is to let him have fun and a give him a sense of achievement. The rest will come.
The most important part in teaching a 13 year old programming is to let him have fun and a give him a sense of achievement. The rest will come.