Assuming you're corssing the bar under motor, a single rudder is actually better than a twin rudder. Coming in, the waves will be overtaking you. As the wave crest comes under the stern, the water in the crest will be travelling forwards faster than the boat is (particularly if its beginning to break), so you loose water flow over the rudder and so loose steerage.
If you have a single rudder and an inboard motor, the rudder is positioned in the flow of water from the prop, allowing you to maintain a modicum of steerage as the wave crest passes under the stern. You don't get that with twin rudders.
Nearest we have to your bar in this part of the world is Chichester bar, which can get hairy in a southerly. Done it with young kids - as long as they're clipped on, and you're not trying to do it in stupid conditions, they think its great fun - better than a theme park!