How can a child with Australian passport attend an international school here

My wife is Chinese and I am an Australian with a 10 year green card (previously with a Z for work).
Our son (6yrs old), was born in China and HAD a Chinese passport but 12 months ago we decided to apply for Australian passport which he has used within the last 12 months. His Chinese passport was cancelled. As you will be well aware... now when we leave the country we need a special pass from the PSB so doesnt require a Visa.
OK, now for my question...for him to be accepted at a local school (international class) we are told he needs a valid Chinese Visa. If we obtain a pass and travel back to Australia can we apply at the embassy for one for him ? If so.... what type can we get..?..and would we just show the pass to return and just show it to the school ? Look forward to your advice... SAM