How do young children learn ideas about size, quantity, and grouping?

During the preschool period, which aligns with the preoperational stage (ages 2 to 7), children learn about their environment primarily through symbolic thought, language, and mental imagery.12

Regarding concepts like size, quantity, and grouping, preschool children typically approach these tasks based on concrete, perceptually attractive physical features rather than abstract logic. For example, when evaluating quantity, a preschooler may focus on the external shape of an object rather than its actual volume or mass. If presented with two equal amounts of clay, a young child might incorrectly conclude that a long, thin piece has more clay than a round ball because it looks different.31

Because their thinking is intuitive and egocentric during this stage, children often struggle to perform logical operations, such as understanding that quantity remains constant despite changes in appearance (a concept known as conservation). They also have not yet fully developed the ability to perform seriation, which is the systematic arrangement of objects by size or weight. These more complex logical abilities, including the understanding of number relations and hierarchical categories, typically emerge later as children transition into the concrete-operational stage.12