When a child is born, grandparents consider how they should be addressed by the new bundle of joy. Should they be Grandma? Grandma Sally? Gigi? Nana? Mamaw? Any of these are fine, and perhaps calling each set of grandparents by a different name makes sense to the child and helps differentiate them from one another. But there really is no question as to how parents should be addressed by a child, even if the parents’ relationship is no longer intact and there are new significant others involved.
Children come with two parents, only two. Whatever the child calls each parent when the relationship is still intact is what he/she should continue to call their parent afterwards, whether this is Mommy or Mom or Daddy or Dad as in the case of heterosexual couples or Mommy and Momma Jane, for example, as in the case of a same-sex couple. When the parents end their relationship with one another and introduce a new partner, that new partner should never be called the same name as the parent. Never. That name is reserved especially for the parent and should be protected.
A frequent response to this is, “But [the child] started calling my wife ‘Mommy’ so we figured that’s what she wanted to do.” Maybe the child wanted to, but you as the parent have the responsibility to direct the child that Mommy is actually the child’s mother and only Mommy should be called Mommy. Significant others and step-parents should be called by their first name, or some other nickname that is NOT Mommy or Daddy.
Worse yet, new over-zealous step-parents may inadvertently create anxiety in a child and conflict between co-parents when they tell the child to call them Mommy or Daddy. Being married to a parent does not make you the child’s “New Mommy” or “New Daddy”. That is the stuff of movies and fairy tales. There is no new or old Mommy or Daddy. There is only one of each parent, and that relationship should be given the proper respect.