Why does the mummy call her mother?

In English, it is customary to add -y at the end of a word to express a nickname or a bit of a slur. The same is true in Chinese. Sometimes we tease children and call dogs puppies when talking to them...

The same is true in English. For example, when pup is called puppy, it actually lengthens the sound of i:, which is easier for children who are new to learning the language.

So mum becomes mummy.

In fact, the word mummy is also transliterated, so it has nothing to do with it...