Often children memorize how to assemble a stacking tower just because of the colors, not the size of discs. This tower will teach to distinguish the sizes, and the colors will merely help. It is much more interesting to play this way!
Build figures on a flat surface. For example, a caterpillar or a snowman
Imagine that the discs of the tower are stars (the way we see them from the Earth). Some of them are closer and bigger, others are further and smaller. Make constellations (existing or imaginary) with them
Set wheels in motion. Which will roll further? In which surface: upwards, straight or downwards?