Neutralising child rotations -> Parent

I need to transfer the rotations of a child gameobject to the parent gameobject. In theory this should result in the same orientation/position for the child object?

The problem is that that when i perform the swap (transfer of rotations) the game object appears to move slightly. What is the best way to transfer rotations from child to parent. neutralising the child rotations?

e.g.

 Quaternion qVals = new Quaternion(childGameObject.transform.rotation.x,
                         childGameObject.transform.rotation.y,
                         childGameObject.transform.rotation.z,
                         childGameObject.transform.rotation.w);
                     
 childGameObject.transform.rotation = Quaternion.identity;
 parentGameObject.transform.rotation = qVals;