Combat your Prejudice
The area of blended families is the last frontier of socially sanctioned prejudice. There are activist groups for most sub-populations of Americans. The one population who gets the most legal and social prejudice is step-parents and step-families. I think this is the most insidious place for discrimination. If I write this post within my intentions, I will insult you little and motivate you to do better.
If it is okay to discriminate at home, then how easy does that make it to do it elsewhere? On top of that, we are basically modeling to our children that we CAN and SHOULD prejudice people who are not genetically related to us. Ok, to put that in perspective: how much of the global population to you claim as your genetic family?
It's not just that step-parents succumb to prejudice, so do the children. But, I'm talking to adults and adults are the ones who need to be the "bigger people." I get it. You were a stepchild once and your stepmother mistreated you. And then, low and behold, you find yourself married to a person who has kids from a previous marriage.
The visceral reaction is to play out those unhealthy dynamics with an INNOCENT child. Your feelings and memories are valid. But they are not valid in this new environment. Don't get me wrong, every one has their pain and needs grace. But, for the love of your spouse, this largely innocent child, and the future of the marriage that holds together your present family, keep your past in your past.