Our almost-four-year-old son was playing with his blocks the other day and I was rather impressed by the design layout he set up in his room. First, he pulled the blocks into color sets so each "building" would be a single color. Then he started building.
It was the middle of the day so we were distracted and running around with G, and when he was done, after each one, he would call us in. Check them out. (Ignore the messy room...it was Saturday, ok?)
I don't know...but there is purposeful symmetry, asymmetry, and balance in all of these. Some stronger than others, but I don't think I built anything like this at his age.