Clearly that depends on place and class, and frowned upon by who?
Usually by those who had smaller families of 1-3 children, 4 at most.
Because there were tons of big families already in existence when I was born, and many more were breeding like rabbits despite desperate housing situations, especially Catholics, and specific races.
I think you’ve kind of answered your own question - those doing the frowning would have shown attitudes like this, eg ‘breeding like rabbits’ rather than, ‘how lovely to have a large family.’
In the 60's child benefit was only paid on every second child, specifically to encourage replacing the lost war generation. If child no.2, 4, 6, 8 died, it didn't make financial sense to those on a low income, to not replace it.
No, child benefit (family allowance) was paid for the second child because there was child tax allowance for the first. It was a minimal amount so no real incentive to have children.