Ok here goes, I am a American citizen living in Australia. My visa ran out a yr ago so basicially I am not supposed to be here. In the time I have been here I have married a Aussie woman and we have had a son who is 7 months old now. I was wondering can we fly to the states with her only having a tourist visa? Also what steps can I take to get my son US citizenship. Also she has a son from a previous marriage that we will be bringing with us. Any help would be appreciated and hopefully someone here has been in a similiar situation and can give me a guide on what we need to do.

Yes you could Visit the USA with her having a tourist visa, but cannot stay in the USA and adjust status, a proper immigrant visa will be needed, either IR-1 or K-3. Consider the CR-1 it does not take much longer than K-3.

You register the birth at nearest US consulate, they will then issued a US passport for child.

http://travel.state.gov/law/info/overseas/overseas_703.html

Too bad you overstayed in Australia, if you were there with residency you could have filed for the spousal immigrations visa directly to the US consulate, and saved a bunch of time as compared to filing for in in the USA.