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I suspect you have something in the puffball group, but still very immature and so I cannot be sure from the photo. Since you are in Victoria I think you should contact the Royal Botanic Gardens in Melbourne for further advice (https://www.rbg.vic.gov.au/science/identifications/fungi-identifications/). You may need to send them specimens. What you see above ground are the ephemeral fruiting bodies, their functions being dispersal of spores. The bulk of the fungus consists of a network of fine threads in the soil and is present throughout the year. Furthermore, many fungi form mutually beneficial symbiotic associations with plants, the thread network being attached to plant roots for exchange of nutrients. By now that thread network is well-established and you don't necessarily need any more spores. Should you want to remove the fungus it is that network that must be removed. The trouble is that it could be quite extensive and so removal might require removal of a lot of soil - and this question remains: Have I got it all? Hence I tell people that in most cases removal of a fungus is impractical.