GUI should not be child of the Camera... If you want a smooth camera movement in relation with the character, or if you implement camera shake (very very comon), you would end up moving also the GUI, and thats not usually desired effect.
The best way for all GUI imho is to add them as childs of a CanvasLayer
node, so they always stay fixed in the screen, no matter what happens to the Camera, player, or whatever other node.