Wow, Thanks for the info! Can't digest it at the mo as a cold has me in it's grips...bleary brain, yuk. Cheers JaxHello and welcome :)
As said above, partner visa is an important thing. Current processing times were running at about 8-9 months for an offshore application. Perhaps work out costs and see what you think of it all.
Download and print off the partner visa PDF. Go through it carefully, strike out all the parts that don't apply to you. So fiancee stuff for example. Makes it easier to digest when you realise chunks of it are not for you :)
Get busy getting your son his Aus citizenship by descent if eligible and then his Aus passport if its not done already. That should take no more than a couple of months, maybe a bit more. It is far cheaper and easier (and safer for your son) than adding him to a partner visa application and paying all those fees etc. You will need it when your OH applies for a partner visa as your son will have to be listed but not actually applying. So proof of Aus citizenship and Aus passport will be expected.
If you've any questions on the partner visa process give me a shout. Its a pretty straightforward application but can look overwhelming when you first look at it all.