The way benefits and taxes are calculated,have come under serious criticism lately, not undeservedly so.
We seem to have a "cliff edge" system i.e. if you earn under a certain threshold you pay x tax on everything above your personal allowance,if above you pay y on the same entire amount!!!
I think the child benefit along with other entitlements does need tweaking , i understand in the case of a couple it is still being paid regardless of total income -then the higher earner pays a progressive tax on earnings as a means adjustment.
At present we seem to have totally seperate departments dealing with Tax,National Insurance and benefits and it often feels to me as though "never the twain shall meet!!"
Hopefully the universal credit system will simplify things-but why not send your views to your local MP,so he/she can look into this,as i think your question is a good one.
You may initially receive a standardised answer but any MP worth their salt, in my experience could bring your suggestion up up next time benefits are on the agenda.