I have a foster son, who today loudly and quite seriously proclaimed that he's not my real kid. He's lived with us for over a year, and we are most likely going to adopt him, having started the paperwork to do so. I normally don't care much if he talks about his birth parents, or if he calls me by my first name, but for some reason, this just bothered me today. Thanks!
Don't worry about it. That's a really common behavior with foster kids. Here are a few of the many reasons why:
Foster kids aren't always sure where they stand with foster families. He may simply have thought it would be taking too much liberty to call you his "real" family.
Some foster kids still hold out hope of their birth parents showing up able and willing to care for them. Calling you his "real" family might, to him, mean giving up that hope.
Some foster kids think that it is disloyal to their birth family to give you that status.
Some foster kids don't get that you would have any feeling about it at all, and are just trying to be precise.
Some foster kids have been tossed around enough that they feel like calling you their "real" family prematurely would jinx any chance at adoption.
Or, it could be any number of other things. Don't sweat it. :)