My other two call me mama.
From baby through toddler stages, DS called me Mama, which I loved. Then he spent at least a year calling me Mommy, which I didn't like. Now for the past couple years (DS is 6), I'm both Ma and Mama. There was only a month or two in there where he experimented with calling me Mother, which I really didn't care for (thanks, Looney Tunes!). I never in a million years would have expected to be called Ma, but it sounds way more natural now than Mommy or Mother.
DS used to call DH Daddy, but now it's almost always Dad. Mom is only used to denote relationship--X's mom, so DS never addresses me that way (although it's what DH and I grew up calling our mothers).
My son is older so he calls me mom (and DH dad) but when he was younger he called me mommy (and daddy). I wanted him to call me mama and tried to get him to, but he just couldn't pick up on it. If we ever have another child, I'll work harder on it.
Kara - Homeschooling mom to Greyson (13), three lazy cats, two hyper dogs, and 11 crazy chickens. Loving our life on 5 acres in the middle of nowhere. TTC #2 for over 12 years. Soon to be a stand-in mom for foster babies!