Long Weekend Suggestions

Am looking to get away with the family for New Years long weekend. I got 3 young kids and would like suggestions that isnt too far from north east Adelaide suburbs. Maximum 3 hour drive, budget $300 including petrol. Camping is ok but must have facitilities for the little woman. Dont wanna go up the river as we can't relax for fearing the kids are near the drink.Can you suggest Caravan Parks? National Parks? Tourist Attractions etc etc