I don’t have an “official” answer, but these are certainly facts:
(1) Wherever civil authorities have approved/formalized “gay marriage,” including custody of minor children, “parenting” of minor children – through reproductive technology, heterosexual reproduction of convenience, and adoptions – even the civil authorities have no legitimacy in removing the children of such households. In fact, as it is right now, parenting is a free-for-all, and has unfortunately been for some time. Single women can become mothers & head up households via IRL or anonymous sperm donors who abandon their biological responsibilities. Same for cohabiting straight partners, etc.
We have never had formal prohibitions against even inappropriate straight parenting, but that’s because so much more of society had (a) common sense (b) less available, reliable contraception (c) much more of a sense of personal honor & an internalized moral code (d) the heterosexual married state was the overwhelming approved environment for parenting; there was significant social disapproval of unstructured arrangements for children.
(2) The RCC has no civil authority to remove the children of gay “parents” – however those children, sadly, were created or acquired.
(3) The real conflict comes, i.m.o., in catechesis and sacramental initiation. No matter how charitable in manner we are commanded to be to all people, I don’t see how any priest faithful to the RCC can seriously call the “parents” of a young baptismal candidate the candidates’ “two parents.” They are not. They are the child’s guardians. They are either one biological mother & one adoptive mother, or one biological father and one adoptive father, and thus they are not a whole parental pair. Or they are two adoptive guardians. They are not parents, plural, in the definition of parenthood, which specifies two different genders as patterned in nature.
In catechesis, as others have mentioned, it would be necessary to instruct in moral theology. It puts a child of such a relationship in an uncomfortable & conflicted position to hear about how his or her guardians’ relationship is fundamentally disordered & prohibited. But a faithful catecheist, priest, bishop, would have no other choice.
As others have noted, the situation creates scandal, as – by not addressing it - it tacitly approves of an unchaste cohabitating relationship by members of the same sex, while demanding moral compliance from heterosexual parents. This also creates morale problems for other parents – for example, at a Catholic school. Suppose there is a divorced mother who has found a loving patner & stepfather for her child, but must wait for an annullment before formalizing any such relationship (rather than cohabitating). Why should she and he be bound by the moral law, while not the “gay parents”?
It is a morally incongruous situation which demands resolution and equity.
I find it incomprehensible that a supposedly Catholic gay “couple” – even if acquiring children by adoption & not assisted technology, and even if supposedly living chastely – would formally participate in a Catholic life while cohabitating. It sets up a double standard (as already described), since cohabitating straight couples would be assumed to be sexually intimate, even if they claimed chastity.
So the only option for such a gay Catholic “couple” would be to live chastely & live apart and not to initiate guardianship over children, by any means. What’s the point, then, in announcing oneself as a “couple”? Get real. You’re not allowed to be truly a couple in RCC moral theology. You’re also not allowed to acquire children through the kind of assisted reproduction which would be necessary for biological acquisition. It seems to me that an honest choice has to be made: Do you want a truly Catholic lifestyle, or do you want a more active or more intimate, or more apparently intimate, gay lifestyle in which no church cares whether or not your partnership arouses suspicion, creates a sense of injustice, etc.? Because the truth is that the two lifestyles are incompatible.