This is a really short but to the point article I found on the Empowering Parent Website…..might be helpful to some.
Does Your Child Say This? “You’re not my mom! I don’t have to listen to you!”
by James Lehman, MSW
When you’re raising or helping to raise a child that is not biologically your own, whether you’re a stepparent in a blended family, have adopted or foster children, or are bringing up your grandchildren, kids may sometimes use this fact against you during the heat of an argument. When a child says “You’re not my mom or dad,” what they’re really trying to do is take the power away from you. Focus on what your role is: caretaker. That means you should inform the child what the rules are in your house. The whole idea here is to avoid a power struggle. What the child is doing is inviting you to a fight. And remember, you don’t have to attend every fight you’re invited to. Avoid the power struggle, and calmly state what your role is and what the rules are. It’s very important that you verbalize no judgments about the biological mother or father. Judgments will only lead to more anger and resentment, which will lead to more power struggles.