Let's get one thing out of the way right now – you shouldn't bring your children. They might want to go, but unless they have a very high tolerance for a long movie (2 and half hours) and an abnormally high tolerance for what might be the most frightening performance ever (Heath Ledger's Joker), I'd get a sitter.
Now: this is some incredible movie. Ledger is that good and so is the film. But get your tickets now because it's selling out.