Final answer:
Preoperational children cannot comprehend that objects can be in more than one group due to a lack of capacity for class inclusion, a concept defined by Piaget during the preoperational stage of cognitive development.
Step-by-step explanation:
Preoperational children lack the ability to comprehend that objects can be simultaneously part of more than one group. This inability is indicative of a lack of capacity for class inclusion. Piaget referred to this deficiency as a limitation in the preoperational stage of cognitive development, which typically spans from ages 2 to 7. During the preoperational stage, children engage in symbolic play and develop language skills, but they struggle with tasks that require an understanding of object conservation and class inclusion. For instance, they might misinterpret quantity if the physical appearance of objects changes, such as thinking that more pizza pieces equate to more pizza, regardless of the actual size of the slices.