Scratch, Alice (and variants), Stratch NG, Unity3d (Score 1)

I've found Scratch to be very accessible for kids starting around 7. http://scratch.mit.edu/

The visual programming language was used by Lego for the Mindstorm platform, as well as others. I believe there is an Arduino front end too.

Scratch TNG is a 3d version of Scratch tilted to simulation.

Alice, Storytelling alice, and Alice 3 are all nice. Alice3 has an onion-skinning mode where the visual programming language can be peeled down to the underlaying Java code in a series of discrete abstraction steps.

Unity3d, recently made free, would be another step along. A non programmer can get somethings to happen pretty easily. Underneath you are scripting in a javascript variant, python, or C.