I see...problem is, that this isn't possible in that way, because an Object3D doesn't know it's children. It only knows it's parents. I suggest to use World.getObjects(), iterate over the enumaration and store all objects in a list where Object3D.hasParent(<yourObject3D>); returns true. That will give you all the direct children of your object. If that's not enough, you'll need some stack or recursion to collect them.