As far as I understand it, if you are supporting her child/children then you have every right to claim child benefit on your own behalf, but don't be surprised if they insist on paying the money to her, as the mother of the child/children.You will also be able to claim Child Tax Credit and Working Tax Credit and although your wife cannot actually make a claim in her own right, she will be included as joint claimant on your claim form.
It's a bit of a nonsense really, she is not legally allowed to claim but as your wife she must be part of your claim.