I have heard of kids who call their parents by their given names. It seems disrespectful to me.
Some time ago Lindsey decided she was going to "try out" calling me by my name. She said my name and looked at me out of the side of her eye, waiting for a reaction. If I just told her not to call me that, that'd be all the more reason to try it out. So instead I told her this:
Anyone in the whole world can call me by my name. My friends, people I work with, even people I don't even know can call me by my name. But only two people in the entire world have the privilege of calling me "Mommy," and that's you and Marissa. And that makes that name VERY special.
She never tried calling me anything other than variations of "mommy" again.