I’m a young mom with a pre-teen son and he’s called me “mommy” up until he was about 10 and a half. Since then he’s been calling me “Ma” which I find pretty cute. Especially when he extends it to “Maaa” when yelling from another room. Maybe it’s a southern thing lol. Just curious about what y’all call your moms?
“Mum” is a shortening of “mummy” (or similar) which almost certainly came before “mother” (or its ancestor words) as a word for one’s primary female caregiver if not also birth giver, on account of it being baby-talk that ancient parents naturally took to be a name bestowed by the child.
In languages descended from Proto-Indo-European, the -t(h)er suffix is a familial grammatical particle that has long since ceased being productive, and remains frozen in all daughter languages. Speaking of which, the -ter of “daughter” is the same particle.
That “mum”, at least phonetically, is also an abbreviation of “ma’am” is a coincidence caused by dropping so many sounds from the original “ma dame” that it reverts to, well, mumbling, which isn’t far off baby talk, all things considered.
FWIW, there are places in the world where “Mam” is a name given to mothers by their children, which is also rooted in baby-talk and also has no connection to the other pronunciation of “ma’am”.