I teach year one and for the last two years my theme has been Around the World. I have picked countries that the children would be interested in eg Japan, Hawaii, UK, Holland, Africa. If you back to the old boards there are lots of posts on this topic.
If you choose to do Australia only country that is also a continent there is a lot to do. Examples our original settlers Aboriginals. There are lots of dream time stories. They are ideal for smaller children. Look at some of our great places to visit eg Great Barrier Reef, Ulura,
Mem Fox is a great Australian author. Use the book Possum Magic which has two possums going around Australia to visit all our capital cities and eating Australian food on the way. In my studies we have also cooked a national dish for us try vegemite sandwiches, ANZAC biscuits etc Songs Don Spencer and others have songs about our animals which are unique. look at words that different but mean the same eg footpath, bin, our spelling of colour,
My kids love finding the countries in an atlas. I have just bought some that are suitable for small children that have pictures across the maps. if you want any other ideas on Australia email me. Both my classes last year and this have loved the topic thats why I did it again.
A book my students love is "The Armadillo From Amarillo". This story talks about how we live in a city, in a state, in a country, on a continent, and so on. Great book for introducing the topic. To help my kids learn the continents, we just remembered that that one starts with E (Europe), and the rest start with A. We have the Ellison dies for the continents and made a concentration game (sillhouette on one card, name on the other). Maybe you could use xerox copies to do the same. Good luck!
North America married South America and they went to Europe for their honeymoon. Soon after, they had quadruplets, who all had A names: Africa, Australia, Asia and Antartica. Cute story to remember the continent names.