Final answer:
Children lacking conservation skills might think the quantity changes when a sandwich is cut into halves. Conservation skills develop in the concrete operational stage, enabling children to understand that appearance changes do not affect basic properties like quantity.
Step-by-step explanation:
Children who lack conservation skills would assume that a sandwich cut into two halves has more quantity or is different from its original form. Conservation is the understanding that altering an object's appearance doesn't change its basic properties. In the developmental psychology of Jean Piaget, conservation skills are typically seen in children during the concrete operational stage, which is usually developed between the ages of 7 and 11.
Before reaching this stage, children may believe that changing the form of an object changes its quantity as well. Using examples like a square peg fitting through the square hole and a round peg fitting through the round hole of a children's toy can illustrate the concept of shape conservation.
Moreover, the principle of reversibility which is understood in the concrete operational stage, suggests that objects can be changed and then returned back to their original form or condition. For instance, when water is poured from one glass to another of a different shape, the amount of water remains the same despite the appearance of more or less due to the shape of the container.