I'd tell the authorities if I knew something was going on (not on gossip).

Why?

I don't work when I have a baby and pay taxes (OK so I currently don't but DH pays loads of tax) and struggle so you can defraud the system and have an easy life. I struggle and do the right thing. You have it easy and cheat. Taxes are too high without people pushing them up even further. We may have had our child tax credit calculated incorrectly after giving the correct information: if this is the case, we have to pay it back (and we rely on this money). But cheat and don't give the right information - we could have done this last year and be getting 5 times as much - then that's NOT RIGHT. Sure you may have to struggle but that doesn't mean it's OK to cheat.

And if you're going to cheat hundreds of thousands out the system then I'm pleased you have to pay it back.