I want to teach my son (4.5 years) "programming" (obviously, too early for general-purpose programming, but a limited-environment language can certainly be taught). I'm considering writing my own little language/"interpreter". Is there anything already out there that's worthwhile? The options I've seen is Scratch (8-year+) and Logo (seems boring to me for this age). Some others are listed here http://en.wikipedia.org/wiki/Educational_programming_language , I haven't checked all of them out though (e.g., Karel looks intriguing).