The longer I observe children and blocks, the more respect I gain. This lad for example is experimenting in ways I never dreamed of – and definitely learning about symmetry and geometry in the process.
Too often blocks are viewed as a "toy" to be left behind when children move to primary school. In fact, this is the age when youngsters are becoming most deeply involved! I've seen six-year-olds invent fabulous narratives with blocks and watched a twelve-year-old achieve architectural feats.
If you want to foster creative imagination, literacy, and hands-on learning of maths, physics and design, allow your children ample time with blocks. Then observe the truth of Einstein's words that "Play is the highest form of research."