Added getChildren to keep inline with Group

src/gameobjects/DisplayList.js

@@ -176,6 +176,19 @@ var DisplayList = new Class({
         return gameObjects[gameObjects.length - 1];
     },
 
+    /**
+     * All members of the group.
+     *
+     * @method Phaser.GameObjects.DisplayList#getChildren
+     * @since 3.12.0
+     *
+     * @return {Phaser.GameObjects.GameObject[]} The group members.
+     */
+    getChildren: function ()
+    {
+        return this.list;
+    },
+
     /**
      * The Scene that owns this plugin is shutting down.
      * We need to kill and reset all internal properties as well as stop listening to Scene events.