Utilitarianism and Morality

Most utilitarians say you shouldn't try to be a utilitarian. You should follow the sorts of common sense rules that would forbid torturing children, because following those rules will actually lead to the greatest good. But i think the utilitarian still has to accept that in exceptional cases, it could well be right to torture some child to prevent abon oing. The question is how to balance partiality towards oneself with impartiality.