Cognitive Developmental Theory
Although there are many different theories of cognitive development, we are referring here to Piaget's Cognitive Development Theory. According to Piaget. His theory of cognitive development is a "stage theory" which has several stages of development, and in each stage of development, children are faced with challenging situations which they must deal with and overcome through increased mental abilities. Once the challenge is successfully dealt in that stage, the children can move on to the next stage of cognitive development.
This is similar to Erikson's theory of psychosocial development, but this is a cognitive theory...it's based on cognitive challenges and cognitive advancements by the child which allow them to overcome the challenges. After each new stage is reached, there is a plateau during which the child/person is able to think in new and more advanced ways. For example, an infant can't think in abstract terms like you can because you have reached a more advanced stage of cognitive development and a higher stage in Piaget's theory.