Lithgow - less than 1 1/2 hrs driving a bit slow up hills (not at all crowded, easy access by dirt road + easy-medium-hard 4x4ing everywhere around it). Read my review in the Australian Park Reviews section. - viewtopic.php?t=255
- also has a really nice bushwalk to a old train tunnell with glow worms in it.
Mt Watagan - about 2hrs driving fast (freeway), not usually that crowded except on public holidays, but even then u can just go find your own camp ground (i have a secret spot on a clearing at the top of a hill
) this too has a range of 4x4ing but most spots are easily accessible. Not much in the way of activities (besides 4x4ing), has some nice bushwalks around the main campground but no reall creeks afaik.
Colo - Really close, like 45 mins - 1hr, with a river to swim in (but u pay and its crowded on holidays) and to my knowledge, no real 4x4ing.
Janolen caves might be a tad more than 2hrs but well worth the trip. I havent been there in years but what I do remember it was great.
The best place i could reccomend as far activities for kids go, would be Mungo brush. Its about 4hrs drive though, but u can camp with 200m of the beach, drive your 4x4 on the beach, and then there is also a freshwater lake u can swim in just about 700m in the other direction, its awesome
If you want more info on any of these spots post your questions up here, or PM me. I'm heading up to Lithgow on Australia day if you want a tour guide