The child benefit is for the benefit of your children. It is not your personal source of savings. So yes I can quite understand him objecting to you squirrelling that away while he pays for all child costs out of his salary or inheritance. (You don’t say how old your children are but it sounds like for a long time he was covering all costs? And what proportion is he now covering? And is it easy to cover everything the children need or a strain?).
As a separate issue, if you gave up your ability to earn, with his agreement or encouragement, in order to raise your DC, then you need financial security and you should not be treated as if you can’t spend any of the family money. You need to come to an agreement with him about how that is all arranged, so indeed you have some pot of money (not the child benefit) for your personal spending.
right now, you are basically laying claim to the wrong pot of money, because you have nominal control over it, in order to avoid having the right conversation about how to organise your finances.
if your husband is abusive/ controlling, this may be the only option, but no it’s not the ideal way I’d arrange it in a healthy, functioning family.
the money is paid by the government to the mother, because it is far more likely to be spent on the child that way - and that is what it’s for. If that is best kept in their interest as an emergency fund if you have to leave then go for it… but it’s not for make up in my opinion.