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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def add_children_to_node(self, node):
 """ Add children to etree.Element `node`. """

        if self.has_children:
            for child_id in self.children:
                child = self.runtime.get_block(child_id)
                self.runtime.add_block_as_child_node(child, node)