Going with the baby for a walk, you offer him to collect different stones. Usually this proposal is perceived with great enthusiasm. The pebbles come across big and small, black, white and variegated, smooth and rough.
At home you thoroughly wash, dry and put them on the table, and maybe on the floor.
Carefully consider and feel the pebbles with the baby, explaining which of them more, some less, some smooth, some rough. Then ask your child to choose the largest stone, the darkest, smoothest and Vice versa.