Hi Nick,
Welcome to the site. I haven't posted many threads so am quite a novice here too but thought my experiences might help a little. Everyone on this site is so helpful and friendly, and you can actually pick up a lot of information by doing a search and reading old posts.
I was lucky enough to obtain citizenship by descent last summer as my mum was born in Sydney. I have two daughters who are now eligible for permanent visas but this is only the case as they are both under 25 (they are 15 and 17) and are considered financially dependent on me. Looking at your post I'm not sure if this would apply to you, in which case you may need to think of a different route (which I can't help you with - sorry).
I would suggest you have a good look on the Australian embassy website - try this link
Child Visa (Offshore) (Subclass 101)
I'm really not an expert in this - like many others on the site I've just spent the usual number of hours trawling the web trying to find the answers. Give the embassy a call if you can't find the answer you need - they are really helpful but it does cost £1/minute!
Good luck!