Carseats in Australia

We travelled to Melbourne a few years back and packed our baby car seat and a booster seat. We even plastic wrap the box to ensure it would not get too wet on arrival. The box was huge and the check in counter wouldn’t allow us to check it in as normal baggage. We check in as a cargo. Upon arrival we took out box cutters that was supplied from the plastic wrap counter that was wrapped together within the plastic wrap to open the box.