[Cognitive] child development

As children get older their thinking becomes progressively more sophisticated, advancing through a series of fairly definite stages that appear to be associated with an increasing ability to handle generalization and abstraction. It is not clear whether this development is primarily associated with physiological changes or with the accumulation of more experiences (or, in effect, with the addition of more layers of software). Nor is it clear how it relates to the fact that the number of items that can be stored in short-term memory seems steadily to increase.