Backing up bibliolept.Grandparents get called what the grandkids call them.
Bigger granddaughter, 8 years old, calls me poppy, pops or pop. MrsP is granny.
Smaller granddaughter, 16 months old, calls me bappie just now. MrsP is nannie.
I have to say, though, that it would be unusual for a grandmother to be called mama.
Mothers have reserved that particular combination, and variants of it, for themselves.
Agreeing with the others, and adding that sometimes the name for "Grandma" is tied to how far the grandchild's speech has developed.
For example, when my grandson was just learning to talk:
- If I was not present, his mother was "Mama".
- If I was present, his mother became "Mommy", and I was "Mama".
- My husband was "Papa".
Now that he is four and his speech has developed into four-year-old jargon:
- His mother is "Mama".
- I am "Dramma" (rhymes with "grandma"; he hasn't got the "gr" sound down yet).
- My husband is still "Papa".
Sometimes a particularly cute nickname will stay long after the grandchild has grown. My grandmother was "Grammamom" for the rest of her life.