Allow for children to be explicitly included in ranges.

src/oscar/apps/offer/abstract_models.py

         Default display_order for a new product in the range is 0; this puts
         the product at the top of the list.
         """
-        if product.is_child:
-            raise ValueError(
-                "Ranges can only contain parent and stand-alone products.")
 
         initial_order = display_order or 0
         RangeProduct = get_model('offer', 'RangeProduct')
         """
         Check whether the passed product is part of this range.
         """
-        # Child products are never part of the range, but the parent may be.
-        if product.is_child:
-            product = product.parent
 
         # Delegate to a proxy class if one is provided
         if self.proxy:
         if product.product_class_id in self._class_ids():
             return True
         included_product_ids = self._included_product_ids()
+        # If the product's parent is in the range, the child is automatically included as well
+        if product.is_child and product.parent.id in included_product_ids:
+            return True
         if product.id in included_product_ids:
             return True
         test_categories = self.included_categories.all()

tests/integration/offer/range_tests.py

         self.assertFalse(self.range.contains_product(self.prod))
 
 
+class TestChildRange(TestCase):
+
+    def setUp(self):
+        self.range = models.Range.objects.create(
+            name='Child-specific range', includes_all_products=False)
+        self.parent = create_product(structure='parent')
+        self.child1 = create_product(structure='child', parent=self.parent)
+        self.child2 = create_product(structure='child', parent=self.parent)
+        self.range.add_product(self.child1)
+
+    def test_includes_child(self):
+        self.assertTrue(self.range.contains_product(self.child1))
+
+    def test_does_not_include_parent(self):
+        self.assertFalse(self.range.contains_product(self.parent))
+
+    def test_does_not_include_sibling(self):
+        self.assertFalse(self.range.contains_product(self.child2))
+
+
 class TestPartialRange(TestCase):
 
     def setUp(self):
         self.assertTrue(self.range.contains_product(self.parent))
         self.assertTrue(self.range.contains_product(self.child))
 
-    def test_cant_add_child_product(self):
-        self.assertRaises(ValueError, self.range.add_product, self.child)
-
     def test_included_class_with_exception(self):
         self.range.classes.add(self.parent.get_product_class())
         self.range.excluded_products.add(self.parent)