Mommy or Mummy?

My son and I were taking a walk the other day and having a talk. I was trying to explain that he will be spending alot of time at his Auntie Sharon's again, but not because "Mommy is sick" and "Mommy still loves you" and "mommy this" and "Mommy that".....so on and so forth. So we were talking and continuing the conversation and shortly Trevor asked if I could stop saying "Mommy" and I asked "Why?" He stuck out his arms and started moaning like a Mummy. I couldn't help but laugh.