There are so many good comments here already. RMAC, great job opening the door to honest communication with your DD. IMO, if she's old enough to ask about the AA books, she's old enough for an honest discussion on the topic, at a level she'll understand.
Coyote, thanks for sharing LMC's thoughts. Wow, did that make me cry. Kids take in so much more than we adults give them credit for. They are amazing, aren't they?
I've pretty much kept it to telling DS, who is 5, that his daddy has an illness called alcoholism. I have and am struggling with deciding whether to explain more or not. Not yet, I think, but like LMC, I think he has a pretty good idea of what it means, just not the technical jargon.