We drove down at Christmas time and the kids were 5, 3 and 1 so it is definately doable. We will do it again after Christmas this year as it is just too expensive to fly.
We overnighted in Port Macquarie on the way down but this was only because we didn't get away from Bisbane until nearly 10am. We dove all the way through coming home as we left at 6 am. We stopped probably almost every 2 hours, some of these were just toilet only stops and others were longer where the kids could run around and have a play in the park and stretch their legs. We didn't seek out particular destinations to stop, just when we felt we needed to.
It is a good drive now with several bypasses and if you have two drivers it won't be a difficult drive.