I thought this was going to be another article about kids watching Peppa Pig. My three year old has a sort of mixed vocabulary, but mostly from watching Matilda, the Musical on repeat.
I ended up with Ted Kelsey, personally.
"Hehehehe... Stiletto, I'm so clever..."
The writing on that show was top tier and holds up well today.
I've thought "mommy" vs "mummy" was a spelling difference. The words sound the same to me, /'mɐmɪ/.
But either pronunciation of "mummy" (embalmed corpse) is how I would address my mother as a child: https://en.wiktionary.org/wiki/mummy
"Mom" always sounded like "Nom" with an M.
But yes, it's "mahmmy", which is only very subtly different from a British "mummy" - in the American version, there's almost a hint of an "r" at the end of the vowel, whereas the British version has a straight (and short) "u".