Cerebral Palsy is not one disease or illness. 'Cerebral palsy' is a term used to describe a condition where the effected individual has a persistent but evolving movement and motor functions disorder that is secondary to there being a non-progressive brain abnormality present.
In simple terms: as a result of a brain injury the child suffers a physical condition that effects their movement, this physical condition evolves as the child grows on a spectrum of severity.