So why is that my fault?

As Moroni is enjoying his new job in a new city, I get to enjoy all the moments with our children...ALONE!  I do mean ALL moments.  Tonight as I sent our third daughter to her room for not listening for the 100th time I got to over hear this conversation...
(Madelyn crying)
Ellie: "Madelyn what's wrong?"
Madelyn: "Mommy put me in my room and took away 'de de'"(more tears)
Savannah: "Did she take away 'big de de' or 'little de de'?"
Madelyn:(big breath) "BIG DE DE!"
Ellie: "Savannah we should find 'little de de.' Where is 'little de de'?"
Savannah: "Mommy didn't say anything about 'little de de'."(hehehe)
You then hear running from the bedroom to the living room and back again
Savannah:  "I found it!!"
Madelyn:(big jump) "Thank you Sa Sa!!!"
Savannah and Ellie: "Sorry Madelyn, Mommy shouldn't take away 'de de'"

Wait a darn minute!!  Why is that my fault?  Why is it my fault that they make bad choices and I have to be the "heavy" and punish them.  Why is it my fault that I asked you to do the same thing 100 times and you decided not to listen 100 times?  All these questions kept going round and round in my head.  Until finally I started cracking up and could not stop.  I laughed so I didn't cry.  Then from the other room I hear Madelyn say "Mommy can I come out now?"  Here we go again...