Brian is right, too..
The CAS (Canberra Astronomical Society) would likely be the closest to you, and there's a couple of other canberrans as members here (stringscope and BC) - between them they have a range of dobs (6", 8" and 10" dobs I think), so it might be a good idea to PM them, maybe arrange an observing session with them, or head along to a CAS observing night. I'm sure they'll be glad to help.
You can take your son as well, see how big the scopes are compared to him and whether with a bit of practise, he'll be able to "drive" it.
btw,
to the forum.. How did you hear about us?