Python 3
\nclass Solution:\n    def postorder(self, root: \'Node\') -> List[int]:\n        if not root: return []\n        if not root.children: return [root.val]\n     
```\nclass Solution:\n    def postorder(self, root: \'Node\') -> List[int]:\n        if not root: return []\n        if not root.children: return [root.val]\n        l = []\n        for c in root.children: l += self.postorder(c)\n        return l + [root.val]\n```
['Recursion', 'Python']