We had our 2 oldest while we were living in Ireland. It was very different environment then when we lived back here. They were just starting to get things in place for some kid activities like Little Gym (kid gymnastics), they did not have alot of things like you learn to expect here. There was no ECFE type things there is not a community education where you can sign you kids up for different things. They did have Mom groups or play groups, but it was very hard to find. I knew of 1 breastfeeding support group and 1 of the Mom's was try to get a play group together. In Ireland they start school younger. Kids start Kindergarten at 4. So your little guy might be going into school when you get there.
The really nice thing that we miss alot is the total lack or responsibility outside our yourselves. You don't have a house that needs to be maintained (depending where you live), no yard, non of the other distractions that take you away from spending time with eachother. So at nights and weekends it's all you. It's easy to go on day trips places. Quick pack a picnic and head out for no other reason then you can. We really miss the carefree nature.
I don't know what Australia will have for kids to do. So if your used to being active with alot of people you may want to ask the question. They should have a person that works on relocating people down there. But if your used to finding entertainment by yourself with your kids, that shouldn't be an issue.
It can get lonely without family. Be prepared for that. The important thing is to make friends with people your husband works with or your neighbors. But you'll need an urban family to help you. If nothing else someone to recommend a good Dr. or baby sitter.
Hope this helps a little and I didn't scare you off. It is a wonderful experience living abround. And if you didn't you'll always wonder "what if".
Good Luck, hope you guys get the job. I would love to live in Australia for a few years.