At which stage of cognitive development, according to Piaget, do children begin to understand the concept of conservation, and how does this relate to Kohlberg's moral development stages in terms of reasoning about fairness in rules?

According to Piaget, children begin to understand the concept of conservation during the concrete operational stage, which typically occurs between the ages of 7 and 11. Conservation means that children realize that certain properties of objects, like volume or mass, remain the same even when their shape changes. For example, if you pour water from a short, wide glass into a tall, narrow glass, a child who understands conservation knows the amount of water is still the same. This understanding connects to Kohlberg's moral development stages, particularly the conventional level, where children start reasoning about fairness and rules. Just as they grasp that physical properties remain constant, they also begin to see that rules should be applied fairly, leading to a more mature understanding of justice.