Internal (non-leaf) node of the TShapeTree. This is practically just a list of other children (other TShapeTree items).
All children are considered "active" by this class.
This class owns it's children TShapeTree. Since TShapeTree is a simple tree structure, there are no duplicates possible, that is given TShapeTree instance may be within only one parent TShapeTree. (VRML node's parenting mechanism is more complicated than this, because of DEF/USE mechanism.)