Here's how my preschool visit went:
Some kids experimented with different shapes before deciding what to build:
This would be a good point to demonstrate the strength of the shapes. Triangles stand tall and don't collapse when you push down and them. Squares collapse under the weight of you pushing down on them. Ask which shape they'd rather have for their houses. You can also ask why roofs are triangular shaped.
They had some good building going on.
They learned a little about measuring during this lesson.
**Don't worry if you don't have the time or resources to make a fancy shake table. You can make an easy shake table with two pieces of cardboard, 4 same size bouncy balls, and 2 rubber bands. See Raft's Shake Table on how to construct the simple shake table. Marshmallow structures work for those shake tables too.
I'll post my lesson that preceded the shake table structures in a few days on the layers of the earth and a brief discussion about plate tectonics. They were surprisingly interested in the brief lesson and game I had.