All children are "pure."
But nearly all children are born in sin. I've always wondered what this meant. It merely means that they were born separate from God (except for Yehoshua of Nazareth, and perhaps a few others unknown to history).
All are born with ego and the excess baggage (karma) of prior lives. How else can Christ's statement of "dying by the sword" be true, unless those who lived by the sword in one life fall victim to it in the next? This is what Numbers 14:18 was trying to tell us.
Why was Jacob loved by God in his mother's womb, but Esau hated? Esau was the elder by seconds, but yet he deserved to have his "birthright" taken from him. Why? Perhaps because he took someone else's birthright in a prior life.
The bodies are born with passengers -- invisible, immortal true selves (souls, Holy Ghosts, children of God), within. Their decision to cling to physical methods of perception and control is what makes them vulnerable and thus evil.
They contain the potential to be good, and activate that good by deciding to let go of the physical -- the sense of self-righteousness, self-importance, scarcity, vulnerability and the like. When they assume perfect humility, but perfect confidence (faith), then they regain that viewpoint of walking in the Light of spiritual perception. I was there for several moments in 1971. Forty-one years later, I finally understand what happened.
The spiritual counseling I was receiving had me consider helping others. During those thoughts, I gave up the ego and found myself outside, hovering 15' in the air, looking at the details of the world around me without human eyes. When I became self-conscious of light passing right through "me," I lost my few moments of bliss and returned to the dark and evil of ego.