Final answer:
The preoperational stage of Piaget's cognitive development theory is marked by children's use of symbols and involvement in pretend play, although they are not yet capable of adult logic or understanding conservation.
Step-by-step explanation:
Cognitive Development and Piaget's Stages
The stage of Piaget's theory of cognitive development that is characterized by the active acquisition and use of symbols is the preoperational stage. This stage spans from approximately 2 to 7 years old. During the preoperational stage, children learn to use symbols, such as words and images, to represent objects and ideas. A notable feature of this stage is the engagement in pretend play, where children might imitate airplanes with their arms or use a stick as a sword. Despite their use of language and symbols, these children do not yet comprehend adult logic or have the ability to mentally manipulate information.
For example, when Keiko received a whole slice of pizza and her younger brother Kenny received a slice cut into five pieces, Kenny believed he had more pizza simply because it was divided into more pieces. Children in the preoperational stage lack the understanding of conservation, which is the concept that an object's quantity remains the same despite changes in its shape or form.