Piaget proposed four stages, or milestones, of cognitive development in children:
The influence of Piaget’s ideas in developmental psychology has been enormous. He changed how people viewed the child’s world and their methods of studying children.
He was an inspiration to many who came after and took up his ideas. Piaget's ideas have generated a huge amount of research, which has increased our understanding of cognitive development. The stages outlined above aren't quite correct, and some debate the whole concept. However, his ideas have been of practical use in understanding and communicating with children, particularly in the field of education; indeed the education systems in the UK are all heavily influenced by his theories.
This video clip from a PBS documentary, the Human Spark, gives an insight into the importance of language acquisition in the early years and how as parents we can shape our children's understanding of the world from a very early age.