NSW roadtrip

Without knowing the ages of your children or their attention span, a ticket at the Dubbo Zoo covers two days, and you really need that to see it all. A number of animals, such as the big cats, sleep during the day. Getting there early each morning will give you a chance to make a bee-line to these. There are also Ranger talks as they feed the animals, and two days gives you a better chance of seeing a few of these. One, which costs a little extra, is feeding the Giraffes, and most children love to participate in this hands on opportunity.

Further south of Dubbo is Wellington Caves with three different caves open for guided tours. There is a lovely spacious and quiet caravan park. There is also a children's playground and a swimming pool there.

Coffs is close enough to Dorrigo, so go check out some of the Waterfall Way i reckon. No idea why you plan to stay at Coffs or what your doing for those days, but i'd look at camping out the back of Dangar Lodge at Dorrigo for a few nights myself and go check out that area some.

You could go see the dish at Parkes, Orange is a beautiful place as well

I don't know your circumstances but if you are heading as far south as Wollongong I would consider spending less time up Coffs way as it is close to you and more further south while you have the opportunity

Geez
Coffs to Tamworth is less than 4 hours driving time but you can easily spend 2 days doing it. It does depend on what your family interests are. Things I would consider once you leave Coffs is the millionaires Nimbin (Bellingen), the Tree Walk just before Dorrigo, Dangar Falls in Dorrigo, Ebor Falls just out of Ebor, Point Lookout (1550m) has alpine heath vegetation & Antarctic Beech it is so high, cool and wet. Wollomombi Falls and the 700m drop gorge country 40km east of Armidale (I think Australia's 2nd highest falls).
IF you are into nature you could spend a week around Dorrigo-Ebor.

Tamworth to Dubbo is only 3.5hours driving via Coonabarabran (slightly shorter via Coolah). It is well worth the detour into the Warrumbungles National Park, it's recovering after the devastating bushfires of 18 months ago. The view from Siding Springs Telescope (the largest in Australia) is well worth while, then exit on the western side to Tooraweenah and onto Gilgandra. Going via the Warrumbungles makes it a full day.
Dubbo to Wollongong is certainly doable in a day, approx. 5 hours driving. Would be worthwhile though having a look at the lookouts around Katoomba. Once down the bottom it's onto the M4, then after a while onto the M7 down to the M5, SW towards Melbourne for 20-30(?)km, then left down to Wollongong.

Why so many days in Coffs?

Thanks for your feedback so far guys. It looks like there is quite a bit to do around the Coffs area so thought we would stay a few days. We're meeting friends there who are coming from Geelong. Once we get to Coffs, we both have 2 weeks to get back home. We'd like to to some 4WDing, bushwalking, beach days etc. The only reason we had Wollongong on the list is because a friend lives there. But we may scrap that as it looks like there will be plenty to do further up. I'm just thinking it could be just too much driving also. I'd like it to be a holiday as well, and the kids won't handle being in the car all the time.They're 7 and 9. I'll do some research on the places mentioned above and rethink the plan. Cheers.