Murat, I have just booked the following for a family holiday in March. It looks very promising for both night time astronomy, and day time activities for the kids:
www.barkalafarm.com.au/
It is situated 28km north of Coonabarabran, so about 5 hours drive north west of Sydney.
No beaches, unfortunately.
I have also had some wonderful family/astronomy camping holidays at Wee Jasper Reserves, about 4 hours drive south west of Sydney (40 minutes due south of Yass):
www.weejasperreserves.com.au/