Just thought I would post an update after our trip. We stayed at Pelican Point and surprisingly were the only people there at first. The camp sites were quite large but very sparse. There is a toilet block but down by the boat ramp, 800 metres away. I found it a lovely place to stay at. The view across the Coorong was lovely and there were lots of birds, including of course Pelicans. You also have to be self sufficient as there is no water.
My ideas though of spending days there with the kids swimming in the Coorong did not work out. Getting to the water involves walking through a thick, black, smelly mud and the water has a lot of algae in it so not really appropriate for swimming. With our family I think a couple of days would have enough. In hind sight I would recommend camping at 42 Mile Crossing as you can drive across the sand to the ocean beach.