Mine is the opposite situation. BM is a serious PAS case. One of the many tactics she has used on our son (now 10 yrs old) is to make him call his step-father Dad. When he verbalized his dislike for this, BM told him that as long as he was at thier house, stepfather is acting as Dad, and that's what he is to be called.
This really burns me up!
And just for general information, I was considering becoming a foster parent at one time. They gave me lots of booklets and pamphlets to read on rules, regulations, parenting, etc. A lot of the information can also relate to parents and step parents...
One of the things foster parents are NOT allowed to do is let the children call you Mom or Dad. Also, the children should not use your last name, even if its just verbally. It went on to say that even if the kids want to do this, it is your job to not allow it. It gave reasons such as causing identity problems, and causing kids to be more apt to reject thier parents and/or thier heritage.
It also talked a lot about how important it is to become an addition to the kids life, not a replacement.
LittleBit's Dad