I have given this over 3 minutes of thought before I came up with the answer.
It really is a regional issue.
For example, in my home state of Arkansas I am amazed to hear children call their mother and/or father, with the same names that my mother and father used.
I heard a little feller that was lost in KMart call out, 'Hey Mama, Hey Pappy. Where are you?" The very same names that me and my brothers called our mother and father.
In the the Hamptons, out on the veranda on Sunday afternoon as the shadows edge closer toward the lake shore, the children will call out. "Mumsy. Faaaather. May we cavort a bit longer near the shore?