But are they withholding money from the non-vaxxers? Or giving money to the vaxxers?
As my understanding goes, they are withholding it from non-vaxxers.

Why don't I get that supplement? But others on this forum do? Is that fair? (Rhetorical question)
Rhetorical question or not, you know the answer to that. If you are earning enough to not get it, then of course it's fair that you don't because you are obviously in a position where you don't need it

If you want the $700, vaxx your child. If not, sleep with the comfort of knowing you did what you think is right by your child/ren. It's a choice. No one is being forced or coerced.
While I agree with the sentiment that if you choose not to vax then you should also be prepared to accept that you will not be eligible for certain payments and I do think that this will certainly encourage the 'can't be bothered' people to pull their fingers out and get it done, which is probably what the Govt were hoping would happen, I also think that there are some people who do count on this payment for various reasons who may be genuinely undecided about their decision to vaccinate or not. These aren't always the middle class welfare types, these are often the working poor types and there are plenty of them. This is part of a regular payment that they are entitled to, part of which happens to be withheld from them until they get their tax returns done, and now they can't access that money unless they have vaccinated children. It IS forcing them to make a decision. It IS taking away their flexibility to take time to make a decision.