I bought Mia a mini set of a Knobbed Cylinders. She seemed interested in them, so I gave her the simplest set (different width, same height). She nailed it, first try. I popped first two blocks on her shelf but saved others for later.
This is an early sensorial activity. Children are often interested in individual cylinder blocks around the age of two/two and half. It is not necessary to present the cylinder blocks in any particular order, but experience has shown that the child finds Blocks 1 (cylinders varying in diameter only) and 2 (cylinders varying in height and diameter from tall and wide to short and narrow) the easiest because there is a greater difference in the appearance of the cylinders.