I called my mom "Mommy" when I was little, but when we were older we wanted to shorten it to "Mom." She didn't want to be called "Mom" for some reason. She preferred "Mama" so that's what we called her.
My kids call me "Mom" except for my teenager. When he wants something badly , or when he's really hurting (like his appendix on the verge of rupturing) he calls me "Mommy." Sometimes when he's in a really good mood it's "Hello, Mother," to which I say, "Hello, Son."