Have you also noticed that more and more German-speaking people refer to their parents as Mum and Dad when speaking German instead of, for example, Mama and Papa? This phenomenon does not seem to be restricted to those who have a strong relation to the English language, such as bilingual children or people who lived in English-speaking countries, and seems to be more common among young people.
As I do not recall hearing Mum and Dad being used in German when I grew up (I was born in 1979), I suspect the use of these names to have started sometime since then. A very likely origin is the increasing popularity of originally English-speaking TV programmes which preserve Mum and Dad even in their German translation. However, I would be very interested to hear from anyone who can shine a light on this phenomenon.
I have also created a poll asking if you use the English or German form: