I would not worry what that nurse thought about you, not at all. Even if your children were adopted, they would still be "yours". I would probably answer, "of course they are mine, who else do you think they belong to?"
Because we were discussing our kids' special needs, and it was relevant. And I'm not stressed out it; it's just one of those things out there that gives us a little cringe if we think someone took it the wrong way, KWIM? Maggie (in VA)