Find all the children of a node.  must be a undirectional graph with no cycles

    :param node:
    :type node: Node
    :returns: list of nodes
    :rtype: Node[]

def get_children(self,node):
    """ Find all the children of a node.  must be a undirectional graph with no cycles

    :param node:
    :type node: Node
    :returns: list of nodes
    :rtype: Node[]
    """
    if self.find_cycle() or self.__directionless:
      sys.stderr.write("ERROR: do cannot find a branch when there are cycles in the graph\n")
      sys.exit()
    v = self.__get_children(node.id)
    return [self.__nodes[i] for i in v]