I am mostly presenting Montessori work to doll this week. One of which is Geometry solids.
The intent is to teach the child the formal names of these solids. If you are interested, I printed this set of cards here.
Of course, I do not expect my 2.5 year old to know the terms 'triangular based prism' etc. I whipped this activity more for her to do matching which is a pre-math skill. Anyway, I gave her this more for the fun of it.
In David Gettaman's book, I remember he mentioned about allowing the child to explore these solids particularly stacking the solids and showing the child that not all solids are 'stackable' like the sphere. Surprisingly, Doll explored these solids exactly this way without my prompting. In fact, I was trying to pack up and turned around to see her trying to build a tower with the set. Instinctively, she discovered she cannot add more solids above the pyramid (because the base is too narrow- but of course she doesn't know exactly that!) or that the sphere will no stay on top either (because it is rounded).
This is why I love Montessori! There's little need to give extensive explaination- just let the child explore & learn!