Cognition describes the internal structures and processes that are involved in the acquisition and use of knowledge, including sensation, perception, attention, learning, memory, language, thinking, and reasoning.

The Theory of Cognitive Development, one of the most historically
influential theories was developed by Jean Piaget, a Swiss Philosopher
(1896–1980). The theory is considered "constructivist". It asserts that
we construct our cognitive abilities through self-motivated action in
the world.

Piaget described two processes used by the individual in its attempt to adapt: assimilation and accomodation.

Assimilation is the process of using or transforming the environment so that it can be placed in preexisting cognitive structures. An example of assimilation would be when an infant uses a sucking schema that was developed by sucking on a small bottle when attempting to suck on a larger bottle. Accomodation is the process of changing cognitive structures in order to accept something from the environment.  An example of accomodation would be when the child needs to modify a sucking schema developed by sucking on a pacifier to one that would be successful for sucking on a bottle.