Just get this done with all the legal signatures and chops! I can tell you that I, now already 47 years on this planet, have been trying to get a legal and accepted birth certificate for myself for the past two years! Born in Taiwan and no birth registration I am officially non-existent although the Dutch give me a new passport every 5 years.
I don't know how the Australians are (that is the important part if the child is to be an Austalian citizen) but ask, ask, ask and make sure your child will not have any problems 40 years from now!