The time has come the walrus said...
...to open a bank account for the munchkin.
Bankwest have some magical super savery one that I've read good things about so off I will trot tomorrow to finalise the process by showing lots of ID to them and answering a billionty questions.
This also then prompted me to rethink about pocket money etc...
The method I think we'll go with is start on his 5th birthday and he'll get $5- week (which at this point I imagine will go swiftly into his account)
Any extra pocket money can be earnt by doing chores around the house or completeing specific tasks (most likely introduced when he is older and understands a bit more)
I'll also be putting money into his account straight from my pay so he has something in there and can keep earning high interest.
We'll see how it goes and adjust as nescessary I guess.

I'm just hoping he grows up to be better with money than I am and doesn't have the compulsion to see a zero balance in his account as soon as possible. Hopefully these methods will assist in that.
Otherwise he's doooooomed.