One of the problems of means-testing something like child benefit is where to set the bar.
A family with 2 or 3 kids, both parents in reasonably well-paid jobs could well still be very dependant on the child benefit to get through the month. People are, I think, generally loath to go through means-testing & all it involves - loss of privacy, low self-esteem, the unimaginable horror of a neighbour finding out, etc etc. The system in place now helps these people, no doubt about it.
Against that, the couple raking in 500K or whatever get the same benefit, and stick it away for a trip to a health spa or to pay the cleaning lady. They pay their taxes, they have kids, so they're entitled to the benefit.
If they had to stoop (in their eyes) to going along to the Welfare Office to be means-tested for it, they probably wouldn't bother, and wouldn't notice the drop in income.
So where to draw the line? High enough that all who need the help can still get it? What would that figure be? We may find that doing so would exclude so few that it wouldn't be financially viable to operate it - it'd be cheaper to carry on as at present.
As said above, there are many ways to help the less fortunate, should you feel you are being given support you don't need. You can do so regularly, or indeed, as above, put it in a savings scheme to maybe help out with an apartment when the kids go to college or whatever.
But I don't thnk anyone should feel bad about themselves because they don't need the benefit to run their households on a week-to-week basis.