You would be able put childcare costs on your books but I am unsure if you could do this without it being a registered childminder or nursery etc..
I know that it has to be a registered person or company if your claiming through the child tax credits so would expect there to be similar 'rules' that need to be met to put it on your books, the best thing to do is ring the HMRC line and ask them for advice about the situation.