Scratch is a very easy to use and learn language designed by the MIT Media Lab mainly intended to introduce programming to children aged 7-16.

Although Scratch cannot directly control an Arduino, the source code has been modified by another team to produce S4A which read Scratch programs but contains extensions to utilise a subset of an Arduino's input/output facilities.

Links http://scratch.mit.edu

http://seaside.citilab.eu/scratch/arduino

(Site is in Catalan but Google Translate does a good job of converting it to English)