When we give children the opportunity for long periods of uninterrupted unstructured play with open ended building materials they accomplish great feats of engineering.
Building airoplanes in the sandpit with a selection of wood pieces:
Designing marble runs:
that are big enough for a child to sit in:
I'm always tempted to put out something different, something new, something other than we did yesterday for the children.
Sometimes I forget that children need time, time and more time to explore, experiment, discover, invent, recreate, revisit and build on past experiences.
Then I look at what they are doing now with simple old unit blocks, and I remember.