Hi Andrea
I haven't got any children so I can't help you with Teenage Reluctance.
Are you aware that once you get your visa, the whole family will need to travel to Australia (even if only for a very short visit) to validate the visas? This normally has to be done within 12 months of the earlier of the police checks or the meds - the letter granting the visa states the date by which it
must be validated by the act of the whole family entering Australia.
Therefore your son will have had a holiday in Oz by the time mid-2009 comes around even if he has never been to Oz yet. Hopefully the visit will make him think "Beaut."
Also, if anything happens to delay your plans beyond 2009, make very sure that you are aware of the rules for Resident Return Visas. Details are here:
http://www.immi.gov.au/migrants/residents/155/index.htm
The 136 visa permits you to remain in Australia indefinitely, and it permits multiple entry to Oz. However, the travel element of it is only valid for five years from the date that the visa is granted (not the date it is validated.) So when the first five years is up, you will need Resident Return visas if you wish/need to leave Oz for any reason and then go back to Oz. Because of the RRV rules, the idea that one has five years in which to move to Oz permanently can be a bit misleading, I think.
Cheers
Gill