L.P. that's what the theory of structural dissociation posits: that in normal human development the personality structure of the brain is such that it doesn't integrate until a certain point in development. A baby feels and experiences a whole lot of emotional states etc, but has not yet developed a sense of self - a self-knowing, if you will. The infant or young child experiences and feels, but doesn't organise those experiences or emotions into a cognitive narrative or attribute them to 'self'. Those experiences and emotions, good or bad, simply 'are'. In normal human development the personality doesn't fully integrate into a single, stable and solid sense of self until around 6 years of age.
So trauma that happens in those first six years greatly disrupts the normal integrative development of the brain. This is especially so when the trauma comes form primary care givers - the infant or young child is unable to integrate the trauma, so the self and the separate emotional states (and knowing states) remain separate. One single sense of self that owns all of the experiences and emotions never emerges.
So yeah- it is split from the beginning.