We might all agree that young children begin to develop geometric concepts when they are able to identify simple shapes, not simply by memorizing the words of the shapes but by recognizing the attributes of a shape by its characteristics (a triangle has 3 sides- and is therefore, by definition a Triangle).
Solid shapes are a little bit harder and slightly more advanced in terms of defining attributes. When a circle is 2 dimensional, it is a circle. When it is 3 dimensional, it is a sphere. This bucket of Geometric Solid Shapes supports the young child’s emerging concepts of 3-dimensional shapes. They can be sorted, classified, and counted based on color, shape, size or attribute. They might seem too advanced for the smaller children, but I guarantee, that some of your kids are ready for this manipulative.