G'day Wardy,
As it's going to be a family event, I'd start with clermont and the gemfields.
Clermont has the designated fossicking areas, i.e. you don't have to know anyone to get access, you just need a licence.
If you luck out on the yellow at Clermont, it's a short drive down to the gemfields where you'll be sure to get a sapphire, then you wont be going home empty handed.
As Loamer mentioned there are lots of places around the rockhampton area that gold has been won. However they weren't all alluvial as his book stated. I have been lucky enough to have spent a fair bit of time around the canoona and oaks view (my grand parents actually owned the property where the old oaks view mine was) area. The canoona alluvials were the only field that was actually alluvial, you can see a monument dedicated to it about 35km north of rockhampton. Where the alluvial fields were is on private property though. There were reef mines associated with the canoona area as well oaks view, last chance, brittania and satan being the more famous.
A large amount of gold was also won from the Mount Chalmars & Cawarral areas, early reports state that alluivial was short lived and soon gave way to reef mining, however good money was made from this area.
Boldercombe, Struck Oil and ofcorse Mount Morgan are also some good areas, they pulled over 262 tonnes of gold (between 1882 and 1981) from the Mount Morgan mine alone, the best assays recorded (it was a hard rock mine) showed 3,700 oz/ton!
Area's around Raglan (Mt Hiron area) have also had small propects over them in the years.
Ridgelands and Morinish have had large areas of alluvial prospecting done on them too (far too many and far to wide spread to list).
Let me know the area your interested in going and I may be able to help.
cheers
JC