The developmental biologist Jean Piaget named four stages of cognitive development. The first two stages, also known as the sensorimotor stage and preoperational stage, span the ages of birth to 7 years. Each stage contains certain cognitive milestones that mark early childhood cognitive development. As you watch your child grow from infant to toddler to preschooler, you may recognize some of these cognitive milestones as he explores the world around him.
Infants come into the world and enter what is called the sensorimotor stage of cognitive development. The sensorimotor stage is marked by discovery as babies begin to explore the way their physical bodies interact with the world around them. According to the Tela Communications website in an essay on Piaget's Stages of Cognitive Development, this is the stage where infants recognize the concept of the separate self and begin to realize that the world around them is not an extension of themselves.
During the sensorimotor stage, infants learn the concept of object permanence and begin to understand that an object or a person still exists even when they cannot see it. An infant who has learned object permanence may cry when his mother leaves him with a sitter, because he knows that she still exists and has simply left him with somebody else. Likewise, an infant who hasn't learned object permanence may lose interest in a toy when it is hidden from view. The infant with an understand of object permanence will actively search for the hidden toy.
As children progress from infants to toddlers, they also progress from the sensorimotor stage to the preoperational stage. The preoperational stage includes transductive reasoning. According to information on Piaget's Theory from Michigan State University, transductive thought involves seeing a relationship between two things that are not actually related. Your child may be using transductive reasoning if she tells you that an orange is a ball. Because both the ball and the orange are round, her transductive reasoning tells her that they both must be a ball.
Children in the preoperational stage may display signs of egocentrism. Toddlers are notorious for thinking that the world revolves around them, and it's because they are unable to see situations from any view but their own. Many toddlers and young preschoolers simply haven't grasped the concept of another person's point of view, and this may make them seem demanding to parents or other adults. If your toddler walks up and takes a toy that his sister is playing with, it may appear that this is mean or bullying behavior. From your toddler's perspective, this behavior is justified simply because he wants the toy, and he has no awareness that his sister's feelings are hurt. Children typically display less egocentric behavior as they approach elementary school age and begin to learn sharing and compassion.