Take a tree and set the children according to the parents.

        Takes a tree structure which lists the parents of each vertex
        and computes the children for each vertex and places them in.

def find_children(self):
        """Take a tree and set the children according to the parents.

        Takes a tree structure which lists the parents of each vertex
        and computes the children for each vertex and places them in."""
        for i in range(len(self.vertices)):
            self.vertices[i].children = []
        for i in range(len(self.vertices)):
            for parent in self.vertices[i].parents:
                if i not in self.vertices[parent].children:
                    self.vertices[parent].children.append(i)