Who says "mummy" and "daddy"?

Is the use of the terms mummy and daddy to (informally) refer to one's parents particular to a specific socio-economic class or culture? How does this contrast with the terms mum/ mom, and dad?

I can definitely personally attest to it being used by lots of working class families, middle class families, families who would be "old money" by a lot of people's standards but don't have titles, and aristocratic families where there's still ownership of the estate (as opposed to "well yeah, I'm a baroness, but it doesn't mean anything and I don't use it", though that would cover my partner, and she grew up with that use too).

There's definitely a regional element to it. My using those terms wasn't remarkable for a working class kid where I grew up, while my partner's using them did mark her as middle class where she was.

In my experience, it's the working class that have the strongest regional variation; middle class kids have a mummy throughout the UK and Ireland bar a few with a mum and a small number having a mother, while working class kids may have a mummy, but may have a ma, mam, mammy or mum. Moms seem to be more common than they were, suggesting a US influence.

The tendency to use the terms into adulthood seems to have a similar relation to both class and region; some places marking one as working class, some places as middle class, and some places giving nothing away.

Kate Fox in Watching the English claims that using mummy as an adult is upper class while using it as a child is common to everyone.