Thanks for the book recomendation! I'll definitely look for it. After sitting down and thinking hard last night, I realize that the issue here is my own, not his. What I mean by that is that I've come to expect him to "just know" everything. It sounds terrible but I think you guys all know what I mean. But in this case, he really is 6 and relates to the world by how it applies to him. Because of the foster kids he knows that not everyone has great parents, but he believed that all kids were just placed with people like us when there was an issue. We talked a little more last night, he shared with the older kids at the dinner table.
My first reaction yesterday was "OMG, I'm raising a sociopath!" Now that I've had time to reflect, I realize it's lack of exposure more than anything. That I can take care of.