it's a difficult calculation - but is definitely on a sliding scale based on your income estimate
if you go to the centrelink website you can run an income estimator to see what your FTB and child care entitlement is going to be

it wont' give you a dollar amount. it will give you a percentage. the percentage is of the maximum rate of about 3.60 per hour. the percentage you get will depend on income estimate and the number of kids you actually have in care (if you have one child in care one week, 3 the next, you'll get a different rebate for the two weeks)

if you're both working you'll then get half of the out of pocket costs rebated. out of pockets depends on how much the child care centre charges.

it really is messy!