Before the loss of innocence the average child has an inner vision absent to most adults; it's generally stripped away by the age of six. Under the influence of early public education a socialization or social conditioning process takes place, and conventional thought forms take the place of the child's inner thoughts.
Most Blake students remember the vision of the angry God that Blake found in his window at the age of four. You can be sure that such a fancy is likely to be trained out of a small child-- in most cases but not in Blake's. We know very little about his parents other than a generally dissenting faith (Swedenborgians, Moravians, etc.).
But they must have had liberal ideas about child rearing because a few years later when he reported seeing a tree filled with angels, his mother talked his father out of a disciplinary response. Another liberal idea was their permission for him to leave school after the first day (when the schoolmaster flogged a boy).
All this leads to the conclusion that Blake never lost the faculty of inner vision, which has been conditioned out of most of us. With no hindrance to his childhood visions and freedom from organized schooling Blake became an autodidact; in all likelihood regarding pre-Enlightenment thought he became the most learned man of his generation.
Jesus is reported to have said, "Whosoever shall not receive the kingdom of God as a little child, he shall not enter therein" in Mark 10:15. That's often thought to mean that the child trusts his father, but might it not also mean he has a child's imagination?
One might say Blake remained like a child his entire life. The four year old who had seen the angry God in his window, who a bit later had seen the tree full of angels continued to see those sorts of things as the years went by.
In the course of time the 'angry God' became Nobodaddy and a large variety of other 'god-like' figures. And the 'tree full of angels'? who knows.
How could that be? Unlike you and me Blake (after the first day) never went to school, the place where most of the 'child' has been drilled out of us. For Blake? no! "I must Create a System or be enslav'd by another Mans". He didn't heed what the priests told him about God; he already knew the God within (the Quaker Way). He spent twenty years wrestling with the God he knew.
In Songs of Innocence he gave delightful portraits of the child within himself, and in Songs of Experience he showed us what this cruel vale in tears where we live had done to those lovely children. Look at Version 1 and Version 2 of Holy Thursday and at Version 1 and 2 of the Chimney Sweeper.
The Little Black Boy showed a child put upon by a cruel society, but not embittered thereby. Blake's poetry is often bitter, ironic, satiric, condemnatory! "Blake's poetry has the unpleasantness of great poetry" (T.S.Eliot). So much like Isaiah and Jeremiah: pages and pages of bitter excoriation.
But in the midst of the cries, just like Isaiah, you suddenly find passages of ethereal beauty and joy. Like a child: either delighted or miserable!
Finally the child is creative! I haven't found any poet who matches Blake's creativity; his System is like discovering another planet.