Remember the episode of "Everybody Loves Raymond" where the older brother finds out he was concieved out of wedlock? Instead of fudging their anniversary, they fudged his birthday, so all of a sudden he discovered he was a year older than he thought. You could always tell your daughter she's only two.
Several thoughts on family secrets:
My cousin was born seven months after her parents were married. My grandfather claimed that she (over 8 lbs at birth with a full head of hair) was "premature."
My great-uncle died when I was six. When I was seventeen, I found out that while he did, I suppose, technically die "of Alzheimer's," the official cause of death was self-inflicted gunshot wound to the head. And he took his live-in girlfriend with him. This was quite a shock. When I asked my mom about it, she said, "You were too young to understand when it happened, and it never came up after that."
I also found out when I was about nineteen that something happened when I was very small, which is pretty much the only thing I won't discuss with anyone. This is mainly because I have absolutely no memory of it, even though it seems I should. Suffice it to say that I never believed in repressed memories before then, but now I do. I was terribly upset when this skeleton emerged from the closet, but at the same time I understood why it had never come up before -- Mom thought I must remember and just didn't want to talk about it. It's been almost ten years since I found out and I'm still not comfortable with it. But it's an uncomfortable kind of thing -- far more traumatic than discovering that your parents felt that a binding legal contract wasn't necessarily a prerequisite to starting a family together.
Re: adoption, my in-laws had a similar response when it came to Pedro's oldest brother. He was to be the first of several adopted children, because they believed they would not be able to have any "homemade" kids. It turned out they were able to have four more, but they were always open about it and as a youngster the oldest actually lorded it over the younger kids because he "got chose." He also tried to convince one brother that the younger could be adopted into another family, but the older could not be because "I have already been adopted, you can only do it once." Hilarious times.
Finally, we have been struggling with the decision of whether or not to keep Little P's autistic status a secret from him. Clearly, everyone in the family knows, but we're not sure if he will benefit from understanding that he's different, or if he'll feel held back by the label. Further complicating our decision is the fact that our nephew, who is seven, is also autistic but has not ever heard that label applied to himself. He knows that he talked late, went to speech and occupational therapy, and needs special help in the classroom, but he doesn't know his exact diagnosis.
I'm worried that if Little P gets to be a teenager and discovers the label on his own, he'll be angry at us for not having told him. But I don't want autism to be an excuse for poor behavior or lack of academic effort. Especially if he turns out to have typical siblings -- is it more damaging to compare yourself to others whose brains are structured in fundamentally different ways, or to expect less of yourself because you know you have a disability?
So, in other words, AD, I don't know what you ought to do. But if you figure it out, let me know.