Terrain detail children not showing

Hi forum, I'm not sure if this is the right place to post, but there it is : a simple problem with no simple solution as far as I know.

I'd like to paint terrain details with prefabs that contain child objects. But what happens is that only the root object displays, and none of its children. This problem seems to have been reported here.

Is there a workaround ? I really don't want to change my meshes to mold everything into one single root object...

 

Up... I can't believe that no one has had to deal with that problem here, this still looks like a major drawback in the Terrain component...