It’s a sticky wicket, not formally ruled upon by the church.
The Church has declared in-vitro itself to be immoral because it disrespects the human right of all persons to be the outcome of the love between their parents.
But in the question of what can/should be done with children ALREADY existing, but in frozen storage, there is no clarity yet.
There are good theological arguments on both sides. Myself, I think if you choose to adopt and implant one of these children in such a way that you are clear that your action is a rescue and not an endorsement of what put the child in jeopardy in the first place, it is morally good and possibly even heroic. If you do it as a way of sidestepping church teaching against in-vitro… that’s problematic.
Oh, what ARE they? In-vitro normally involves the ‘harvesting’ of numerous eggs from the hopeful mom. They then collect a sperm sample from the hopeful dad and combine the whole mess in a petri dish (so to speak). Many embryos then form and the scientists separate them into individual test tubes. Mom and the doctors decide how many they want to inject into her (often more than she’d be willing to carry to term) and the rest get tossed in the freezer. Many, perhaps most in-vtro patients wind up with more embryos than they want. Pretty gruesome to those of us who consider life to begin at conception.