The code is only needed to decided whether to show the "this container has no children" message. So finding descendants is fine as that still means that it has at least one child. However, it may be that your logic is more accurate, as it would work even if the xblock doesn't render its children for some reason. Do you know if that logic will work for all xblocks? 

There's actually a further issue which is what to do for a container xblock that has no children but does have an interesting rendering of itself. Currently, my code will hide that rendering to show the 'no children' message. I'm fairly sure that Cale would say that we should show whatever the xblock wants to show.

For now, I think I'll stick with what I have, but I'm open to discussing it.