Always call draw for children

gfx/prop/children.lua

@@ -91,11 +91,11 @@ function Children:with(elementType)
 
   function elementType:draw()
     local dirty = Element.draw(self)
-    if dirty then
+    if Element._isDirty(self) then
       self:_getWindow().clear()
-      for _,child in self:_iterateChildren() do
-        child:draw()
-      end
+    end
+    for _,child in self:_iterateChildren() do
+      dirty = child:draw() or dirty
     end
     return dirty
   end