I went ahead and answered the question as best as I could. I told her that sometimes parents don't stay together, and if they marry someone else then the new person becomes a step parent to the kids. She didn't quite get what I was saying — probably because all she has ever known are two parents who stay together and never speak about separation in front of the kids — so I approached it from a different angle. 

I told her this: "If mommy and daddy decided they didn't want to be married anymore, and then mommy eventually married another man, that man would be your stepdad." This seemed to clear it up for her, but I looked over at my husband and realized that I had just painted a picture of one of his biggest fears. Before I could say anything else, my horrified husband said to my daughter loudly, "...but that's not going to ever happen, sweetie, so don't you worry about it."  

I think this wins for most awkward conversation I've had in a while. 

The thing that really amazed me was that my daughter didn't seem particularly alarmed by the whole concept. I'm not naive enough to think that she could care less if we stay together or not, but it was certainly a surprise that she was so easily able to accept the fact that sometimes parents just don't stay together. I guess that sometimes I don't give my daughter enough credit for how smart she is.

I'm starting to think that maybe a separation would not be the earth-shattering, therapy-inducing event for the kids that I always figured it would be. Of course, I realize that they would have huge issues with the whole thing, and that they would probably fight it all vehemently, but I'm beginning to realize that we would probably all muddle through somehow, and figure out a way to start over fresh.