My vote would be to stay on the coastal side of the Great Dividing Range, as far north as you can get.
Unless you are really far north, the nights will be cool, so for sleeping, put the kids in their jamies, then tracksuits, socks and beanies (if that cold), because they will always wriggle out of their bags.
Packing up our camper at 4am in -10 deg C at Glenn Innes in July is a childhood memory I'll not forget. Freezing and crying in the car for the next 3 hours after the radiator boiled due to ice might have had something to do with it. All the coastal camping we did on that same trip was fine temperature wise.
Please don't feed the Goanna.