I didn't want to admit this but I am also a grandmother(a very young one, of course) and I chose the Portuguese term for Grandma which is Vovo'. Pronounced vuh-vo-ah. Very commonly heard where I come from in Massaschusetts(but don't start calling me Massachusetts Deb). Some kids just say 'voa.
My grandaughters say VO VO. I wanted to keep the Portuguese heritage alive for one more generation.