Hmm. If the child refrences the parent, then we can't delete the parent until we remove the childs reference to it, or remove the child itself of course. So we have to do a postorder traversal of the implicit tree. A preorder traversal as you have here would try to delete the parent while the children point at it.

Im assuming that the OP was using using the only sane way I know of to represent an nary tree in a single table form, that is using a parent pointer list representation. Now these may have been asumptions too far but... :-)