Whilst I don't condone it, I have at one stage installed a child seat in a ute and had a child in it....
I found this in the Vicroads site.
When can children sit in the front seat?

While it is legal it is not safe nor is it recommended. The back seat offers far greater protection in a crash than the front seat so it is recommended that you fill the back seat first.
If children are big enough to use a lap/sash seat belt, use the back seat first.
If in a van/utility, use a properly constructed seat with a child restraint if appropriate, or seat belt.


Can a restraint go in the front seat of van or utility?

It is legal to fit a child restraint in the front of a utility or van provided there is a seat belt and a child restraint anchorage point available.
Restraint fitting stations can install a variety of devices that can ensure the safe operation of restraints in these sorts of vehicles.
If there is a passenger airbag in the seating position occupied by a child using a car seat, it is recommended that the seat be moved as far back as possible while still allowing correct seat belt fit.
If there is a passenger airbag in the seating position occupied by the child, you must not use a rearward facing infant restraint.