Our Fathers road is one of becoming. That royal road begins in Him, not in us. It is not of the will of man, or of blood, or flesh, but originates within Him. The process is one of His power bringing to birth His offspring, the birthing of children.
Power to become = ginomai
Children are not His finished product, sons are. "To as many as received Him, to them gave He power to become..."
The groan of the creation is for the manifestation of the full grown sons of God, not children.
The Firstborn Leader joined to Him by His brothers.