You need a reality check, you are living in a good suburb and can't save anything on $100k a year so that suggests you are trying to keep up with the Jones's which is fine if that's what you want but long term you are headed for the poorhouse and a miserable pension.
How do couples with 3 kids a mortgage and an income of $50k survive? Not sure but many do it.
Like many have mentioned, your income is quite good. If you can't save a huge chunk of that each week, you are really not trying. Here are a few tips.
I don't know Melbourne that well, so can't really comment on the area, but I am sure that if you looked around, you would find an area perhaps a little further out, that will have cheaper rental accommodation.
Daycare, do you need it if your wife is on maternity leave?
Car(s), I am guessing that you have expensive loans on vehicles. Is it possible to downgrade, paying cash. This is an area of possible great savings.
Groceries, Each week I am gobsmacked by the amount of "stuff" people put into their shopping basket. Someone I know told me they throw away a lot each week (they can't be alone). Only purchase what you need. Cut down on maybe the "name" brands. Buy some cheaper cuts of meat and make the expensive ones "treats". Buy in bulk where possible. Make your own "snack packs" by buying full size packets and placing small portions into zip lock bags. Soft drinks are expensive and not very good for you, teach the kids to drink water instead.
Do you smoke? If so, quitting will save a lot of money and you will benefit with better health.
Alcohol: This is expensive. Is there a way to cut down? Maybe buy a bottle to enjoy at home with the wife instead of a couple of drinks at the pub.
Eating out: This is a big one for some families and something where drastic savings can be made if it is something that is done on a regular basis. If you eat out once a week, then drop back to once a month. Or special occasions only.
Lunches/morning teas/latte's: Another one that can save a significant amount. Take your lunch to work. Don't buy the latte. If this has been a habit for a long time, it can be a huge sacrifice, but it is well and truely worth it. Maybe give yourself a treat once a week or better yet, once a fortnight.
Clothing: Wear what you have. Don't buy anthing that is not needed. Can you buy cheaper brands when you do need something? Are you buying kids clothing from Myer, when Kmart will do? Does your wife really
need that new pair of shoes.
Cut up the credit card, or put it in the freezer. Anything to make sure it is out of sight, out of mind. You don't need it.
All of the above are some simple tips to help reduce your spending. They are all easily done without any huge changes to lifestyle. Many of the forum members (if not currently doing so) have done this and much, much more to get them to where they are today.
Now, the final step. Add up the savings. There should be several hundred $$ each week. Set up a direct debit into another account (one it is inconvenient to get money out of) AND DEPOSIT THIS AMOUNT each pay period, whether that be weekly, fortnightly or monthly. Pretend you have had a reduction in salary. DO NOT TOUCH IT! This is your deposit for your first home.
If you take the amount of savings out before you even see the rest of the money it is much easier than trying to find it after you have spent everything. Start today! As you reduce your expenditure, then increase the savings amount.
While doing this, keep coming back to the forum and get educated. In a years time, you should be well and truely on the way to your home.
Good luck.