Their child will be told "it doesn't matter" who is their biological father and it won't, until it does. Are they then planning to find out or cut their child out of their life?
Interestingly for those who say that as adopted individuals or those estranged from their biological fathers, mother matters most. I'm sure biological mother matters HUGELY to all children and you only really find that out if the relationship breaks down or the children are separated from the mother. However, my two children are adopted and we have a lot of information about the maternal side for both up to the point of communicating with members of the maternal side.
My DS is 6 and really wants to know about his "other daddy". For him it may be a same-sex parent thing, but maybe not, maybe just because he knows quite a bit already about birth mum.
My DD is 4 and her ethnicity reflects her birth father and is unusual for the UK. While she hasn't asked as many questions yet, I can see that also being something she feels the need to know about in the future.
Sadly in both cases though birth mum has asked for further communication, birth dad showed no interest, one the SWs lost contact with and had no further way to locate, and one they have contact details for but he does not respond.
So there's us desperately wishing we could find some way for our DCs to have contact with birth parents and then other "non-traditional" parents wanting their children "all to themselves" and wanting to conceal their children's biological origins. Which never, ever ends well. As many late discovery adoptees and children of donor gametes have shown.