I have my minivan, everyone is restrained to the maximum safety - even before the laws came in.
However, my DH has a commodore wagon which we had the dicky seat installed in (3 seater bench seat - 2 with headrests). I have had before my DS2's maxirider in the 3rd row (there is anchor points on the back of the dicky seat), however the top of the seat is only cm's from the roof of the car - and TBH causes a real visibility issue. So I have never done it again. This is the same with my DD's pegasus booster.
Point being that I can't have any booster in the 3rd row...at all!
My DD is only 6 - and DS2 is 4. Are they allowed to sit in the dicky seat at all? The seats are made for children up to 12 years old, and the seatbelts are at a children's placement (they are lower), so I would assume they would be classified as "boosters" in themselves???
In my heart, I know they are safe, however I am worried that a cop would be an a*se and give us a ticket.