Still under construction.
Let's start with Alan Kay's fundamental ground work on user interface design.
We need to have our user interface talk to these three modes of thought in our brains:
doing (the 5 year old kid): hand gestures multi touch speech,
images (the 8 to 11 year old): augmented virtual 3d (using different channels in the brain), rear view mirror driving, zoom world
symbols (11 to 15 year olds):