I think as long as you are honest with all parties and with the child then things will work out. If the donor is unknown, telling the child "I don't know who it is" is telling them the complete truth, which is all our children generally want from us.

Knowing the father and not telling the child is a lie of omission and if the truth ever comes out then I could foresee mother/child relationship problems occurring.

As another poster said, the father's opinion is so important in this too. He may be willing to be a donor, but does he realise that he will have no place in the child's life? Would be still be prepared to be the donor? These details must be straightened out before conception to avoid problems down the track IMHO.

Best of luck with it all

T
xx