Kangaroo Valley - great location, lousy viewing potential. A mate used to live there and said the valley often filled with cloud at night. You'd be better off up on the highlands but it still isn't far enough out to be truly dark.
Wee Jasper - very good prospects. The camping reserve near the town would be great for observing but there isn't much for the kids on site. I know less about the four reserves near the river but they could be OK if they aren't too crowded. We were there one January and those grounds were wall to wall tents. I've no idea about the cabins etc.
Wombeyan caves? I'm not sure about local lights. Google maps street view indicates there might be a few outdoor lights.
Jervis Bay is nice but I'm not sure where would be best. There is very little light pollution but a local street light could ruin you night. If memory serves, the view from the top of the hill on Wreck Bay Rd would be nice but I think the lights of the airfield would interfere. You could go down to the old lighthouse or out to the once-planned nuclear reactor at the end of Jervis Bay Rd. BTW Google maps shows a lot of tracks which are not open to the public. [I did my honours thesis there and I did have a key
I spent weeks in total in the bush above Steamers Beach - then back to a comfy bed each night at Wrights Beach.]
