code: public boolean addChildObject(GVRSceneObject child) {
          if (child.mParent == this) {
              return false;
          }
          if (child.mParent != null) {
              throw new UnsupportedOperationException("GVRSceneObject cannot have multiple parents");
          }
          mChildren.add(child);
          child.mParent = this;
          NativeSceneObject.addChildObject(getNative(), child.getNative());
          child.onNewParentObject(this);
          return true;
      }
docs: Add {@code child} as a child of this object.
  
  @param child
  {@link GVRSceneObject Object} to add as a child of this
  object.
  @return true if child was added, else false