C.W.
Hi M.~
Its a bit of a touchy situation and I understand what your saying. I would just correct him (your 2 yo) when he calls you M. and refer to your self as Mom/Mommy when you talk to him about yourself; have your husband do the same. He will catch on.
I feel children should call you what ever you and they are comfortable with. :o)
Good Luck!
C.