Doing a bit of reading on VIC firearm categories and license etc. and their is a spiel about toy firearms.
This is from the VIC Police website on firearms:
There are a wide variety of firearm-themed items available on the market aimed at children or firearm enthusiasts. Depending on the overall appearance and function of these items, some may be classified as a registrable firearm, a replica firearm or an imitation firearm. These require an authority to possess, carry or sell in the State of Victoria regardless of the intent of the manufacturer.
It goes on to explain what are and are not toys (yeah, really...) and the end result seems to read that if you have a plastic toy gun that's real enough looking you could potentially get charged for a proper firearms offence.
Surely no ones ever actually been charged for having a real looking toy... ?