What do you call your grandparents (or what do your kids call your parents)?

My boys call my mom "Ma" and my dad is "Papa". My in-laws are Grandma Hazel and Grandpa Lowell. I am Mom or Mommy and my mom is "Ma". It's kinda funny because it really throws people off when they hear my kids calling her "Ma". But that is what my dad calls her and all of us kids do too, so it stuck with my boys too.

Here's a little story I just have to share. My mom and my oldest son were shopping when my son was about 3 or 4. My mom told my son to pick out a toy tractor and she would buy it for him. The store clerk said to my son "Wow, you are lucky to have such a nice Mom!"
My son replied, "That's not my Mom! It's my Ma!"
The clerk looked at my mom funny and my Mom had to explain that she was his grandma and he calls her "Ma".