Early in this century, Jean Piaget came up with a revolutionary new idea in the field of psychology, which was this: Children think differently than adults. Up until Piaget, it was assumed by the schools of psychology that children thought as adults. Piaget challeneged this with four basic stages of a child's cognitive devolpment.
From birth to two years of age the infant goes through Piaget's Sensorimotor stage. This stage is characterized by an exploration of the world around them through their senses. Most especially touch and taste. Though the sense of hearing is certainly critical to the devolpment of their language skills, this is not a primary factor in their explorations. Suprisingly neither is sight. This is due to a lack of object permanence on the infant's part. Object permanence is the ability to understand that an object continues to exsist when it can no longer be sensed. It is alos during this stage that an infant begins to devolp his or her sense of self.
Around two years of age the child begins to devolp their object permanence along with an intense anxiety of strangers. This second stage, the Preoperational stage, lasts until around age six. During this stage a child begins to explain those things around them which are incomprehensible by "magic." They truly begin to devolp their imaginative skills and engage in "make-believe." Their sense of self has devolped further, inciting an often fierce egocentricism. At this stage, they still lack many problem solving skills, most notably among them the concept of conservation. The tall thin glass doesn't nessecarily hold more than the short fat one, for example.
Folowing this comes the Concrete Operational stage, which will last until early adolescence. With their problem solving skills devolping, children may begin dismissing "magic" as an explantion and instead want a reasonable answer. Concrete concepts begin to form, but abstract concepts are beyond them. For example, a child could understand that 2+1=3 two is an even number, and adding one gives three, an odd number. The child will grasp any number of these, but the concept that adding one to any even number produces an odd number is still beyond their grasp.
Piaget's final stage, that of Formal Operation is where the young adolescent begins to understand these abstract concepts and yearns to experiment with the world around them.