You know, to be honest, I would answer her questions honestly as she asks them. Kids are naturally curious and as they get answers they adapt and move onto the next thing. I was adopted and I don't remember ever being told, so it was always just a "known". My first reaction re: your DH was he is so scared of losing her. The thing is... I highly doubt that would EVER happen... it's a much more special thing to have been chosen by someone than to "have to love" me... get what I mean? However, having said that he might need to prepare himself in years to come for the "you're not my real dad" line in the middle of an argument. I think that if she finds out of her own accord later on that it will cause and wreak a whole lot more havoc than it ever would be answering her questions now.