Mum and Dad or Ma and Pa?

What names do you use in your family?
Do you think Mum and Dad are becoming more common than Ma and Pa. Can you suggest why there are different names and why there seems to be a change underway.
(Americans may say Mom and Dad.)
Update: So far:
Mum and Dad are the favourites in Australia and US except for Africaans and Hicksville.
Maybe US movie and TV scriptwriters have been misleading the world by throwing in too many anachronistic Mas and Pas.
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