Final answer:
The stage that children typically experience during the preschool years, beginning around the age of 2, according to Piaget's theory of cognitive development, is called the preoperational stage.
Step-by-step explanation:
According to Piaget's theory of cognitive development, the stage that children typically experience during the preschool years, beginning around the age of 2, is called the preoperational stage. This stage lasts approximately from age 2 to 7 years old. During the preoperational stage, children begin to use symbols to represent words, images, and ideas, which leads to engaging in pretend play. They start to develop language skills but cannot yet perform mental operations such as understanding the concept of conservation. This means they may not understand that quantities remain the same even when their appearance changes, such as when a pizza slice is cut into smaller pieces but still remains one slice.