I am Mommy, mama, mom and Pam. I am George (from I'll hug him and squeeze him and call him George) and all other variations. I am occasionally mummy or mum as my husband refers to me as that at times. Just like my son will sometimes say vit-a-mins or Vit-ah-mins. In the end I thought I'd care but I don't. He's going to figure out a lot of things in his life and what exactly he calls me (given that it is respectful) is not worth a battle.
I am a very much pick your battles parent. So in the grand scheme of life it's small potatoes. I understand that for some it's not though.
When he was younger I would ask him, "Where's your Grandmother/Nana/Yaya/Abuela" and one day he just said Nana and it stuck.
MY mom was so happy he actually called for her I don't think she cared what he said.