i would be checking if you're actually eligible for the dependent spouse offset now - if you're a sahm with zero income, you get ftbb - i don't think you can get both.

Part A - Dependent spouse

You cannot claim this tax offset if:

your adjusted taxable income (ATI) for 2010-11 was more than $150,000, or
your spouse's ATI for 2010-11 was $9,426 or more.

You can work out your ATI or go to Rates, calculators & tools to use the online income test calculator.

You can claim a dependent spouse tax offset for any period in 2010-11 that you had a spouse and you met all these conditions:

you maintained your spouse; see What is maintaining a dependant?
your spouse was a resident; if you are not sure, read Are you an Australian resident?
you were a resident at any time during 2010-11
neither you nor your spouse (during any period they were your spouse) was eligible for family tax benefit (FTB) Part B or if one of you was eligible for it, you were eligible at the shared-care rate only
neither you nor your spouse (during any period they were your spouse) received parental leave pay.
if you claimed it for 10/11, given your son's DOB, you should probably check with your accountant in case you're not entitled and you get a debt with ATO



as for the rest of your post - my DH went from an 80k income to nothing overnight when DD was 3 months old. it's not a good feeling at all. we have worked out ways for him to be sahp while i'm at work, but it has meant making a lot of sacrifices to have it work out