You could try Kangaroo Valley, which is near (inland from) Nowra. There's a few places in the valley which have short stay as well as long stay places. You could try
Millers Springs Farm Stay....don't know if they cater for kids as well but they do have some facilities which the kids would like.
You might like it that much there, you'll end up buying a property and moving to the valley
What's best is it's only 2 or so hours from Sydney.