We did this trip up to Wonga Beach four years ago, no children, and had a ball tenting almost all the time. We went up the centre way and back via the coast.

Have the RACV caravan parks book and become members of Big4 and Top tourist. It doesn't take long to recoup the cost of joining as you get discounts when you stay there.
We would head off in the morning and then about lunch/afternoon tea time decide where to stay the call ahead. As it's out of school holidays you should have no problems.
Have stayed at most of the places already mentioned and liked Forest Glen on the Sunshine Coast as it was central byt quiet. On the way back we stayed at Hastings Point, had the place nearly to ourselves, heating on the shower floor and heated pool.

Taking a thermos, milk etc saves on costs and time.
Have a great trip