Such Questions Already

So as you know we adopted our children and they are Hispanic.  Michelle has always seemed to be aware that her skin color is quite darker than others.  She has been known to try and wash the brown off in the tub.  We obviously have explained to her that she is beautiful and that this is how Heavenly Father has created her.  Well, lately she has been trying to figure out who belongs to who.  She's asked questions like "Who is your mommy?" or "Who's mommy is Grandma?"...you get the idea.  We have always been very open with our children that they are adopted and when asked have told them that I am not their tummy mommy.  Michelle has been having quite the questions in regards to her other mom.  We have spent much time talking about their birth mother and why they aren't with her.  One thing that Lonnie and I never want to do is to lie to them about what happened.  Although, going into what really happened with a 6 year old I don't feel is appropriate either.  So we just say that their mommy loved them but made some bad choices, was sick and was not able to take care of herself or them.  Needless to say, we knew that we would have to talk about this issue with the children but never in my wildest dreams did I think it would be this soon.  Although through it all I am still so thankful that I can look my children in the eye and tell them that their mother did love them.  There are so many children that have been or are in the system that this is not the case.  I know that some of you who read our blog have adopted yourselves.  Any suggestions and/or ideas on what you do in these situations?