"Have some thought for those of us who mave moved here and have a great life on 4k"
rofl
I wish I was getting 4k!
-Still at least Im not paying 30% tax/hecs/medicare on what passes for my salary like I was back in Oz ;-)
Getting back to the topic:
Im assuming that the offer is a lot better than your current situation in Aus which is why you are considering it (& of course tax here is heaps less), but of course money is only a minor consideration in terms of happiness, and with 150k you shouldnt have to worry too much about the money situation.
From what you said, I think what you really need to consider is whether your wife will be happy here. If she isnt happy, you wont be either.
Leaving behind all her friends and a familiar environment and coming here will be very very stressful for her, made even more so by the demands of looking after young children. (This applies to you too!)
On the other hand, the chance of working overseas somewhere like Singapore can be a very rewarding experience, and you may all love it.
Having small kids, you will definately want to consider getting a car. You will find the taxis a bother with kids. - no child seats. (Heck, most of em hide the adult seatbelts too!) And they are impossible to get when it rains (or your in a hurry ;-) On the plus side the taxis are very cheap compared to Aus, and you have no parking hassles.
Cars are unfortunately a wee bit pricey here. ie: hows 65k for a hyandai accent sound? Anything over 2 litres costs 100k++. Since you arent given a company car you will have to buy one yourself. Budget 2-3k per month (for a small family car. Forget anything bigger than 1.6litre unless you have money to burn...)