The Open Source KidBASIC project describes itself as an easy to use version of BASIC designed to teach young children the basics of computer programming. It's a strictly line-oriented language, which helps kids easily see how program flow-control works. It has a built-in graphics mode which lets them draw pictures on screen in minutes, and a set of detailed, easy-to-follow tutorials that introduce programming concepts through fun exercises.

It runs on anything from Windows 98 to Windows XP and has very modest resource requirements (48MB RAM and 15MB har disk space). You can find it on SourceForge at:

http://kidbasic.sourceforge.net/