Add a reminder on how to group nodes in the editor in Creating the enemy

getting_started/first_2d_game/04.creating_the_enemy.rst

@@ -22,7 +22,9 @@ Click Scene -> New Scene from the top menu and add the following nodes:
    - :ref:`VisibleOnScreenNotifier2D <class_VisibleOnScreenNotifier2D>`
 
 Don't forget to set the children so they can't be selected, like you did with
-the Player scene.
+the Player scene. This is done by selecting the parent node (``RigidBody2D``) in the
+Scene tree dock, then using the :button:`Group` button at the top of the 2D editor
+(or pressing :kbd:`Ctrl + G`).
 
 Select the ``Mob`` node and set its ``Gravity Scale``
 property in the :ref:`RigidBody2D <class_RigidBody2D>`