Would you tell your child this?

That's really horrible. I don't think that it's appropriate to tell a child that and continuously remind anyone of the experience. I think if such a thing were to ever have happened to me when I was a baby, I'd rather go my whole life never knowing. Especially the whole "first sexual partner" thing, I mean, it's one thing to have told someone about that, but the line has to be drawn somewhere! If I had kids, I wouldn't tell them about it. I really hope you're sister is better now, and it must've been a hard childhood/life having known that. Does your mom know what impact telling your sister this has had on her? I think that this is one of those situations where you can say that, "ignorance is bliss."