[nommm-nommm]

Just one of those words with several different regional pronunciations.

If you can believe Wikipedia - https://en.wikipedia.org/wiki/American_and_British_English_s... - Mom is sporadically regionally found in the UK (e.g., in West Midlands English). Some British and Irish dialects have mam,[117] and this is often used in Northern English, Hiberno-English, and Welsh English. Scottish English may also use mam, ma, or maw. In the American region of New England, especially in the case of the Boston accent, the British pronunciation of mum is often retained, while it is still spelled mom. In Canada, there are both mom and mum; Canadians often say mum and write mom.[118] In Australia and New Zealand, mum is used. In the sense of a preserved corpse, mummy is always used.