Mystery Building Blocks

This toy is based on the idea of building blocks(ie. legos, lincoln logs, etc.). The way that children would interact with them is fairly self explanatory; they can build and create to their hearts desire with the blocks. However, the blocks have polarized magnets built into them, so they can play with the concept of repulsion and attraction. The blocks would also be of different densities/weights, so they can play with weight distribution.

Ideally,  the blocks would appear to be made out of wood. The insides would be filled with different masses, as well as the magnets. They would be extremely durable, ideally able to be played with by infants.