The following article is by the Separated Parenting Access and Resource Center (SPARC) and appears on DivorceNet.com:
When my stepson’s biological dad learned that I was to be the new stepfather, he told his son how lucky he was that he was getting two daddies when most people only get one! When the child came home from that visit and asked me if I was going to be his new daddy, right in front of his biological father, we started to correct him, not wanting to upset his dad. But the father told us what he had said to the boy about having two dads. That took us by surprise, but it did a lot to help us get off to a good start in a working relationship with the father. As a noncustodial parent, now, I greatly respect and appreciate the example set for me by this man. We both continue to have a positive relationship with the son we both love, even though I am no longer officially a relative. I strongly urge stepparents not to try to make themselves into "Dad" or "Mom" without the cooperation of the biological parent, it just gives the biological parent one more thing to get upset about (and rightfully so).