I think it depends on the the level of bullying if parents might need support with this. I think also parents should find out firstly, if their kids are bullying in order to prevent being bullied themselves. By this I mean that some kids go along with the group in order to fit in and are frightened of going against the group in case they themselves get picked on.
But if parents feel they are confident enough and know enough about the reasons for bullying and more importantly the consequences, then they should go for it. But some of the cases I've heard about with regards to bullying did not only involve the parents, but the school and on one occasion the police. So it shows how serious bullying can be and it might be too much for parents to handle on their own.