Do we really need to let the firstborn know they were in vitro? I have no intention of telling the others the method in which they were conceived, other than as a general discussion in how reproduction works — no specifics related to them.
My concern is that keeping this secret will backfire. There is so much out there about secrets destroying relationships if information is disclosed when the child is older.
Incidentally, almost no one knows about our initial fertility issues, and absolutely no one in the immediate family knows.
— Don't Ask, Don't Tell
Don’t Ask, Don’t Tell: That sounds like your primary focus to this point — keeping it from the immediate family, yes? Since that would typically be who does know.
So I’m guessing you need to keep that bigger picture in mind as you figure this out.
Plus, “adoptive/egg donor/in vitro” children have three completely different realities — so even if there were no extended family issues to consider, I can’t see how one answer about disclosure would fit all.
An adopted child of course needs to know about the adoption. Omitting that is a huge lie. One DNA test, and not even within your own family, is all it would take to expose your deception here.
A child from an egg (or sperm) donor is, presumably, the genetic child of one parent and not the other. That, too, is about nothing less than who your child is at a biological level, and withholding that information is also a big lie to tell a child. That, too, is one retail test away from exposure.
A child conceived in vitro with the father’s sperm and mother’s egg is your full biological child, so the in vitro part of it is just mechanics. If you don’t feel like spelling that out, then it doesn’t really rob your child of anything when it comes to identity, and there’s no big unexploded secret waiting to detonate. Sure, say something when the kid is older, because it’s part of his or her story, but there’s no need to race to get ahead of it to avoid the relationship-destroying-secret thing.
Unless I’m missing something here?
I do get a between-the-lines sense that you’re uncomfortable either with sharing in general or with this truth in particular, and I hope that’s not the case. There’s no shame here, no matter what medical assistance you needed. Whatever you can do to become more comfortable with your family’s origin story, or with yourself in general if that’s the root of it, then the better for your relationships all around.
Re: Disclosure to IVF child: You should tell your children when they are older, only so that they are aware they have a family history of fertility issues, which will help them in planning for their own children. Definitely don’t keep that from them, but don’t be ashamed you need a little help to get the family you wanted!