B.K.
I know this has to be very frustrating for you. When I was 10 years old, my dad remarried and my step mom would tell me I had to call her mom if I wanted something. She tried so hard to be my best friend and introduced me to her friends as her daughter. I just want you to know that kids are not dumb at all and I guarantee you your son knows what she is doing and he knows who his mom is. Let her play her games because there is really nothing you can do about it. Don't let your son see that it bothers you. Just be there for your son, and there will more than likely come a time when he wants to share his frustration with you concerning her. I did with my mom.