The relationship between a child and a stepparent is one of the most complex dynamics that exist between two people. Ironically, popular media tends to simplify the stepparent as either the perfect new caretaker, or an evil villain who sees the child as competition. The reality is that most stepparents are caring, generous individuals, who play an important role in a child's development. In addition, most stepparents are sensitive to the fact that they are not a replacement for the child's biological parent. Nor do they expect the children to refer to them as “mom” or “dad”, unless they want to.
The biological parent's feelings are important as well, especially on the all too sensitive topic of calling someone else mom or dad. Most people would agree that this is an issue of respect, but should a biological parent have the legal right to prohibit their children from calling someone else mom or dad? Although it's been rare, this issue has been brought before the family courts. Legal precedence for such motions may have been established in the case of Prince v. Massachusetts, which set forth the right of the government to regulate the actions and treatment of minor children. However, Prince v. Massachusetts dealt with child labor, which is a much more concrete legal concept than what to call a stepparent. Still, it does tie into the question of whether the courts can regulate what a child calls his stepmother or stepfather.
A recent case that dealt specifically with this issue was B.S. v. T.S., in which a mother objected to her son referring to her former spouse's fiancee as “mom”. The judge acknowledged that children have very few rights of self-determination, but that a child's right to call someone mom or dad, when that person is willing to be addressed as such, must be preserved whenever possible. He noted that the situation may be different in the case of infants and toddlers, but the child in this case was old enough to distinguish between his real mother and his stepmother. As the judge saw it, the child came to think of his father's fiancee as a mother figure, because she was very involved in his care on the days that he spent at his father's. His father's household also included three of the fiancee's children from a previous marriage, so there were already children in the household who referred to the adults as mom and dad. Thus, it was only natural and healthy that the plaintiff's son would do the same, and call his father “dad” and his soon-to-be stepmother “mom”.
Because there are very few precedents that deal with this type of issue, the ruling in B.S v. T.S. involved many circumstances that were specific to this particular family. However, specific family circumstances are at the heart of any family law case, which is why it's important to speak to an experienced attorney about your rights and legal options.