To expand on this notion, go on a "treasure hunt" around your house, gathering small objects such as buttons, beads, rocks, coins, and seashells. If your child is under 3, stick with objects that are more than two inches in diameter to prevent choking.
Find a small cardboard box, such as a child's shoe box, and turn it into a "treasure box" by decorating it with colored markers or construction paper. Let your child fill his box with the treasures you've collected. Then show him how to sort his treasures based on different criteria. For example, he might start by separating the buttons from the beads and so on; next he might sort by color or by size. Each time your child has finished sorting his treasures to his satisfaction, put them back in the treasure box for future use.
Sorting is a fundamental skill that requires color and pattern recognition. As your child progresses through preschool and kindergarten, sorting will lead him to an understanding of sets and subsets, one of the fundamental concepts of elementary-school math.
Variety of small, interesting objects (all should be more than two inches in diameter if your child is younger than 3), such as: