Cognition, or cognitive development, includes reasoning, memory, problem-solving, and thinking skills. Young children use these abilities to make sense of and organize their world. By the time children reach the preschool years, their cognitive skills have grown so much that they can engage in complex mathematical thinking and scientific reasoning.

Infants and toddlers play an active role in their own cognitive development by exploring and testing the world around them. Through these explorations and experiments, and with the support of parents, teachers, and other adults, infants and toddlers begin to understand basic mathematical, spatial, and causal relationships. More and more, infants and toddlers can rely on their developing memory to help them make sense of the world. All this activity in the first three years lays the foundation for the more complex cognitive skills children will build as preschoolers.