Teaching children to write software?

Desmond Elliott writes: "I recently worked on a piece of software for an undergraduate course which involved me writing a Sudoku game using the GWT. My youngest sister (9 years old) was fascinated to know how I had done it and seems quite keen to want to know more. I know that some people say that children and fickle at that age but I'm keen to let her have the resources that she needs to learn more about programming if she wants to. Does anybody know about any good resources for children to learn more about Java?"