<p>I think that python is probably an easier first language than many more common first languages (C/C++/Java), so it might be a good choice for your son. There's less seemingly unnecessary odd syntax issues than with other languages. He also might have fun with VPython (<a href="http://vpython.org/)%5B/url%5D">http://vpython.org/)</a>, which is some extension of python which is quite easy to use for graphics. I haven't worked with it much, but its much less of a hassle than graphics in C++ and Java. Different languages are better for different things, so its helpful to know a bunch of different ones so that you can choose the best one for the job. Java and Python are both good choices as they are widely used.</p>
<p>For teaching other kids his age, he might want to look into Alice. (<a href="http://www.alice.org/%5B/url%5D">http://www.alice.org/</a>) I don't know a lot about it, but its some sort of interactive 3-D thing that is intended to interest middle school students (particularly females) in programming, and the researchers claim to have had quite a bit of luck with it.</p>