What negative effects do you imagine?
In essence, the point I am making is something like this: what should the response be if a child is collected by their two, same-sex, parents? Presumably the answer is *not* to ignore it, for fear of allowing discrimination and prejudice; nor can it be to tell the couple that they aren't allowed to turn up together to collect their child. This leaves only one sensible option, which is to address the subject in a fair, balanced, and -- of course -- an absolutely age-appropriate way. That is looking after the best interests of every child, is it not?
But then the further point is, why should only the children who are directly forced to confront this issue because of such unique circumstances be the ones blessed with an education designed to tackle and reduce prejudice? There is no such reason.
The idea that my suggestion is motivated by selfishness is at best utterly wrong, and at worst hypocritical.