I'm going to start a Geography unit with L and E (33 months). Today we did a variation of the Montessori Land and Water Forms activity using real sand and water. Since the girls have no need to know the difference between a Peninsula and an Isthmus (as in the Montessori curriculum), I made up my own variation. We made mountains and valleys, islands, lakes, rivers, forests, and other natural formations that the girls were already familiar with...
L and E already love playing with sand and water (often together), but this activity challenged them to do some thought and engineering to make the different types of land forms (I had to provide some verbal guidance to get them started).
They made some neat observations about how sand and water interact, including the fact that water flows downhill and that water can carve out the sand and change its shape. They also noted the different forces they had to apply to create structures (pushing, digging, packing, etc..), and how dry sand, wet sand, and a water-sand mixture do not behave the same.
This was just a nice little introduction to earth science and creating smaller-scale models of natural formations that are very large in the real world. The next step will be to create symbolic representations of these forms, which will lead into understanding maps.
Of course, you can't do this activity without getting to feel the sand in between your toes: