Jean Piaget was a Swiss biologist and psychologist. He developed his theory of child development by observing children, including his own, in their natural environment. He argued that children had to go through distinct stages of development on their way to independent thinking. Piaget saw play as a reflection of the stage the child is at, rather than an aid to development. The main stages of a child's development as identified by Piaget are: the sensorimotor stage (ages 0 to 2), the preoperational stage (ages 2 to 7), the concrete operational stage (ages 7 to 11) and the formal operational stage (age 11 and up).
The Sensorimotor Stage
Before Piaget's theory, many people believed that children's development did not really begin until they started talking. Piaget observed how babies and young toddlers reacted to faces and to objects, and described the processes as assimilation and accommodation. Objects the child sees and follows with her eyes are being noticed and absorbed. Mobiles and bright, soft toys, such as teddies and other cuddly animals, are appropriate for a child at this stage. Sensory development is at the fore, so the child will touch the toys and probably put them in her mouth.
The Preoperational Stage
The child learns a lot during this stage. According to Piaget, the child cannot yet grasp abstract concepts, and his worldview is still egocentric. However, he is developing a better understanding of shapes and logic, so he will enjoy building blocks and simple puzzles. This is also a stage where language develops, and books, audiobooks and active storytelling will help this process. A child begins to form relationships with other children, and play is a key part of this.
The Concrete Operational Stage
At this stage the child's understanding and thinking is more independent. The child is separating from the parents, and play and adventure with peers is a big part of this. The child at this stage can operate more sophisticated toys and equipment. Children of this age are often highly interested in computer games, but this interest should be balanced with the need to socialize and form functioning relationships with others.
The Formal Operational Stage
Children aged 11 and older still play, but their play is likely to be more formalized -- in the form of sports, for example. This reflects what Piaget called the formal operations stage, where the child is functioning similarly to an adult in many ways, with more structure and rules in her play, and probably less of the imaginative element.